Addressing Concerns for Water Quality Impacts
from Large-Scale Great Lakes Aquaculture

Based on a Roundtable
Co-hosted by the Habitat Advisory Board of the Great Lakes Fishery Commission
the Great Lakes Water Quality Board of the International Joint Commission

August, 1999


Water Quality Impacts from Aquaculture Cage Operations in the LaCloche/North Channel of Lake Huron

by Peggy Gale
Ontario Ministry of Environment, 199 Larch St. Suite 1101 Sudbury, Ontario, P3E 5P9


The objective of this presentation is to share preliminary results of Ontario Ministry of Environment's (OMOE) water quality surveys around cage aquaculture operations in the North Channel, Lake Huron with participants of the Roundtable on Water Quality Impacts of Great Lakes Aquaculture. The presentation will include a brief history of OMOE's role and discuss some of the regulatory challenges in meeting OMOE's mandate to "protect water quality" and surface water goals to ensure that the surface waters of the Province are of a quality which is satisfactory for aquatic life and recreation (OMOE 1994).


Water quality data were collected from nine rainbow trout cage operations in Lake Huron; six from the North Channel, two from Manitoulin Island (Lake Wolsey and Robert's Bay) and one from Depot Harbour, Parry Sound, see Figures 1 and 2.

Lake Huron is a dilute, oligotrophic, low productivity lake which is sensitive to nutrient input. Historic Environment Canada water quality data indicate the North Channel averaged total phosphorus of <5 µg/L, total Kjeldahl nitrogen 0.150 µg/L and dissolved oxygen levels >5 mg/L, one meter above bottom (Stevens et al. 1985).

Figure 1. Cage locations around Manitoulin Island, Ontario.

Note: Manitouwaning Bay site was not sampled by OMOE in 1998, location is provided for information only.

Figure 2. Cage locations in the LaCloche Channel, Ontario.

Note: OMNR 1984-1985 site was not sampled by OMOE in 1998, location is provided for information only. OMNR 1985-1992 site is referred to as the forebay of the LaCloche site.


Aquaculture cage activities began in Northern Ontario in the early 1980s. At this time, sites required a Certificate of Approval for sewage works, under Section 53(1), Ontario Water Resources Act.

In the mid 1980s, OMOE did water quality impact assessments around three operations. At that time it was found that there was minimal impact around the cages, that surface water met Provincial Water Quality Objectives (PWQO) and that there was localized sediment impairment immediately beneath the cages (Bowman 1984; Carbone 1985; Linquist 1986). Cautions were expressed at the time that these studies were conducted under low productivity levels (1-50 tonne fish) and that if production levels increased, impacts would be greater. There was a need for consistency in regulating this industry and a need to develop an appropriate method to determine the waste effluent quality and assess assimilative capacity of receiving waters (Conroy 1983).

Early water quality monitoring conditions required the industry to collect monthly composite samples upcurrent and downcurrent from the cages and analyze for total phosphorus and total suspended solids (TSS). The downcurrent total phosphorus was not to exceed background (upcurrent) by 50% and TSS was not to exceed background (upcurrent) by 100%. There were no requirements for dissolved oxygen profiles nor secchi disc readings at that time.

In 1994, OMOE's legal branch advised Regional staff that a Certificate of Approval did not apply because there were no sewage "works", wastes were neither collected nor treated. Ontario Ministry of Natural Resources (OMNR) then became the lead permitting and licencing agency of the Provincial government. The industry continued to grow in number of sites and expansions at existing sites. OMOE worked with OMNR to get water quality monitoring requirements on the Land Use Permit, offering the industry a "one-window" approach to Provincial requirements.


In the mid-1990s, the public expressed concern regarding the expanding cage aquaculture industry in the North Channel. Public complaints were being received regarding algal growth in the LaCloche Channel. In September 1997, OMOE conducted an inspection of two aquaculture operations in the LaCloche Channel, referred to as Grassy Bay and the LaCloche site.

Grassy Bay exhibited good dissolved oxygen levels in the stratified deeper waters (5.2 mg/L dissolved oxygen and water temperature 7°C). Some dissolved oxygen depletion occurred directly beneath the cages in the bottom 2 meters (1.6-2.8 mg/L dissolved oxygen), but the system was still aerobic. Total phosphorus levels ranged 6-10 µg/L (PWQO, 10 µg/L).

LaCloche site had similar water temperatures 20°C surface to 7°C bottom and the basin was stratified. Dissolved oxygen levels were poor: surface to 12 meters depth were 5-9 mg/L dissolved oxygen, depths greater than 13 meters had 0 mg/L dissolved oxygen (maximum depth 41 meters). The anoxic conditions encompassed the entire hypolimnetic volume over a 250 ha area. Total phosphorus levels ranged from 16-26 µg/L in September and averaged 40 µg/L in October 1997. Secchi disc readings were reduced and an algae bloom was visible.

An August 1985 OMOE survey of the forebay of this area, found hypolimnetic dissolved oxygen levels of >5 mg/L near bottom and total phosphorus levels of <5 µg/L. PWQO for total phosphorus are 10 µg/L (for a high level of protection in waters typically below this level). OMNR manages this area as a cold water fishery and the PWQO for protection of cold water fishery is 6 mg/L dissolved oxygen at 10°C or 54% saturation. The combination of anoxic conditions and high phosphorus loadings resulted in additional phosphorus release from the sediments.

Morphometry of the site indicated that hypolimnetic waters would not readily mix with surface waters (fall turnover was not complete until early November). Depth contours of the area show several distinct deep holes in the basin with steep drop offs (see Figure 3). The bay is restricted in flow both at the inlet (culvert) and the outlet (flowing into McGregor Bay), flushing rate would be low.

The water quality impacts at this location were significant. Estimated 1997 loadings from the cage operation were 1.2 tonnes phosphorus, 7 tonnes nitrogen, and 38 tonnes solid waste. Immediate action was warranted and OMOE recommended that nutrient loadings be reduced immediately and that input of oxygen demanding solids (fish food and waste) be ceased.

An abatement process began in which OMNR and OMOE negotiated with the company and requested proposals to reduce loadings. The company indicated that alternative technologies (i.e., bags) were not economically feasible and the company could not present other proposals to reduce loadings. The parties agreed to a six month phase out of the operation over the winter, so the company could meet market demands. All fish were removed from the site by May 1, 1998 and the Land Use Permit was not reissued.

OMOE conducted an extensive monitoring program of eight other cage operations (plus LaCloche) in 1998 to assess water quality. Sites were sampled during spring turnover, peak stratification (summer) and fall turnover. During spring turnover, all sites had oxygen levels (>6 mg/L) at the bottom and most sites had <10 µg/L total phosphorus (exceptions: LaCloche 20 µg/L and Lake Wolsey 11 µg/L phosphorous(2)).

During summer and fall samplings, impacts varied on a site specific basis, with morphometry and flushing rate being the determinate factors. In some cases, in shallower water (<20 meters), a thermocline would form but surface mixing was sufficient to prevent a hypolimnion from forming. Other sites with deeper (>20 meters) isolated sub-basins, stratified forming a hypolimnion. Other sites were well flushed and their bottom waters mixed well with the main channel.

Figure 3. LaCloche two meter site contours, maximum depth 41 meters (135 feet).

Cages which were in generally 16 meters water depth were surface mixed, which supplied a continuous oxygen supply to surface waters. Oxygen depletion was evident two meters above bottom at these sites (dissolved oxygen <1 mg/L). Dissolved oxygen levels of <1 mg/L were also found in the hypolimnion of isolated sub-basins (except Lake Wolsey, >1.6 mg/L dissolved oxygen). At sites which were not stratified, formed a thermocline and were well mixed with the main channel, dissolved oxygen levels were maintained >6 mg/L.

Individual total phosphorus readings from the perimeter of the cages ranged from 2-36 µg/L, ice-free averages ranged from 7-17 µg/L. Most sites bordered on the PWQO of 10 µg/L.

Overall, sites which were sheltered and had low flushing rates experienced oxygen depletion in the bottom 1-2 meters and some oxygen depletion in hypolimnetic waters of isolated sub-basins. None were as dramatic or significant as the LaCloche site. However, the combination of elevated total phosphorus (above historic 5 µg/L phosphorus) and oxygen depletion at some sites will necessitate abatement and management programs.

Establishing "control" locations proved to be difficult. Lakes or "lake-like" restricted basins would be well mixed during spring and fall turnover and, over the long term, effects from the cage operation would be distributed throughout the lake. In sites which were well flushed, effluent would be diluted quickly, but may have been washed further afield. "Control" locations could be compromised. This emphasized the need for accurate background pre-operational data, including dissolved oxygen profiles from surface to bottom during stratification.

Environment Canada's Lake Huron 1980 cruise data provided historical data for comparison. Zone 1 (Grassy Bay) and Zone 19 (Frazer Bay) covered most of the cage locations with background total phosphorus levels of 4 and 4.8 µg/L and total Kjeldahl (TKN) levels 0.2 and 0.4 µg/L, respectively. 1998 sampling by OMOE showed an increase in total phosphorus and TKN levels around the perimeter of the cages when compared to historic 1980 Environment Canada data.

Current action is focusing on individual site specific effects. Consideration must also be given to the cumulative effects of these operations. Cho (1998) estimates waste output and effluent quality from rainbow trout operations to be: total phosphorus 5.11 kg, nitrogen 30.64 kg, and solid waste 164.3 kg per tonne of fish produced (this is based on low phosphorus feed and best management practices). Estimated yield from eight sites in North Channel and one site in Depot Harbour is 3,000 tonnes of rainbow trout. Based on Cho (1998), this would yield an approximate loading of 15 tonnes total phosphorus, 90 tonnes nitrogen, and 500 tonnes solid waste per year. The industry predicts the production level will double in the next decade (possible 30 tonnes phosphorus loading).

The 1978 Great Lakes Water Quality Agreement states that objectives for Lake Huron are to maintain oligotrophic state and relative algal biomass with a lake-wide target load for total phosphorus of 4,360 tonnes. In 1980, total estimated phosphorus load to Lake Huron was 4,799 tonne (industrial portion was three tonnes and municipal load 121 tonnes)(Dolan et al. 1986). The growing aquaculture industry will be a significant direct phosphorus contributor to Lake Huron and should be included in future Lake Huron phosphorus loading calculations.

Repeats of Environment Canada's ambient water monitoring cruises will help to assess cumulative changes over the years.


Aquaculture cage operations can cause eutrophication, phosphorus increase, algae blooms, oxygen depletion, and localized sediment impairment. Significance of the impact varied from minor to adverse, principally dependant on loadings, morphometry, and flushing rate.

Proper siting of cage operations is critical. This requires pre-operational water quality monitoring, particularly in spring and late summer. It also requires knowledge of site morphometry and an ability to assess the assimilative capacity of the site.

A complete, cost effective, operational water quality monitoring program is essential to ensure continued protection of the environment. Targets should be set to trigger abatement action and prevent adverse effects from occurring. The onus would be on the industry to collect these data and evaluate site suitability.

Inspection and audit roles of Provincial agencies sometimes require that surface water management decisions be made on a limited amount of data. It is critical that operators be required to conduct a water quality monitoring program which will adequately describe the fate of the effluent which they discharge to the environment and its effects on the receiving water. Developing appropriate siting criteria and implementation of an operational monitoring program would be a benefit to both the operator and the environment.


  1. A complete, cost effective water quality management program should be developed with the industry. Operators are responsible for the collection and reporting of data.
  2. Trigger limits should be set on a site specific basis, which would initiate abatement action.
  3. Operators should collect water quality data from potential sites and do a site assimilative capacity study prior to submitting an application for a new site.
  4. An assessment of existing aquaculture effluent and modeling science should be completed and adapted for the Great Lakes freshwater environment.
  5. Environment Canada should continue its ambient water monitoring of stations in the North Channel and Frazer Bay areas.
  6. Cumulative effects and total phosphorus loadings to Lake Huron from the aquaculture industry should be evaluated.
  7. Technologies to reduce waste effluent loadings should be explored.


Bowman, A.B. and J. Linquist. April 13, 1984. Cage Culture Monitoring Programs 1983. Technical Memorandum. Ontario Ministry of Environment, Sudbury, Ontario.

Carbone, J. Nov. 5, 1985. Cage Culture Monitoring Programs, 1984. Technical Memorandum. Ontario Ministry of Environment, Sudbury, Ontario.

Cho, C.Y. and D.P. Bureau. 1998. Development of bioenergetic models and the Fish-PrFEQ software to estimate production, feeding ration and waste output in aquaculture. Aquat. Living Resour. 11(4):199-210.

Conroy, N. Dec. 8, 1983. Approvals Process for Cage Culture Operations. Memorandum. Ontario Ministry of Environment, Sudbury, Ontario.

Dolan, D.M., N.D. Warry, R. Rossman, and T.B. Reynoldson. 1986. Lake Huron 1980 Intensive Survey Summary Report - Report to the Surveillance Work Group. Windsor, Ontario.

International Joint Commission. 1987. Revised Great lakes Water Quality Agreement of 1978.

Linquist, J. Sept. 24, 1986. Cage Culture Monitoring Programs 1985. Technical Memorandum. Ontario Ministry of Environment, Sudbury, Ontario.

Ontario. 1994. Ontario Water Resources Act, RSO 1990.

Ontario Ministry of Environment, 1994. Water Management Policies Guidelines Provincial Water Quality Objectives of the Ministry of Environment and Energy.

Stevens, R.J. M.A.T. Neilson, and N.D. Warry. 1985. Water Quality of Lake Huron - Georgian Bay System. Environment Canada, Scientific Series No. 143.

2. Lake Wolsey in May 1986 (prior to cage operations) was 11 µg/L phosphorous, indicating that Lake Wolsey may not be typically below 10 µg/L phosphorous; therefore, a PWQO of total phosphorus of 20 µg/L would apply for this site.