Lake by lake: Ontario
Erie | Huron | Michigan | Ontario | Superior

Lake Ontario is similar to Lake Erie in length and breadth (193 miles by 53 miles). Yet with its greater average depth (approximately 283 feet), Lake Ontario holds almost four times the volume (393 cubic miles) and has a retention time of about 6 years. The drainage basin covers parts of Ontario and New York, and a small portion of Pennsylvania. Major urban industrial centers, such as Hamilton and Toronto, are located on its shore. The U.S. shore is less urbanized and is not intensively farmed.

Drinking water
Microbial contamination | Chemical contamination | Critical contaminants

Microbial contamination
Regular monitoring of the quality of water supplies drawn from Lake Ontario shows that water quality meets or exceeds public health standards for drinking supplies. Open lake surveillance monitoring conducted as part of Canadian and United States research efforts also confirms the high quality of Lake Ontario water.

The largest category of consumer complaints about drinking water, worldwide, is taste and odor problems. Changes in the taste of drinking water may indicate possible contamination of the raw water supply, treatment inadequacies, or contamination of the distribution system. Although there are standards for some parameters that may cause taste and odor problems, such as phenolic compounds, there is considerable variation among consumers as to what is acceptable. Aesthetically acceptable drinking water supplies should not have an offensive taste or smell.

Although there are no drinking water restrictions on the use of Lake Ontario water, some nearshore areas, such as Rochester and the Bay of Quinte, report occasional taste and odor problems. Lake Ontario water suppliers most commonly receive consumer complaints regarding an "earthy" or "musty" taste and odors.

Studies conducted by Lake Ontario water suppliers have shown that these problems are related to naturally occurring chemicals, such as geosmin (trans, trans-1,10-dimethyl-9-decalol) and methylisoborneol (MIB), produced by decaying blue-green algae and bacteria. Using chlorine to clear water supply intakes of zebra mussels may also stimulate the production of these taste and odor-causing chemicals. Geosmin and MIB can cause taste and odor problems for sensitive individuals at levels as low as one part per trillion (ppt), well below the detection limits of the analytical equipment currently available to water authorities (2 to 3 ppt). Once identified, taste and odor problems can be eliminated at water treatment plants by the use of powdered activated carbon or potassium permangenate.

Taste and odor problems are more common during algal blooms. Additionally, storm events precipitate these problems by breaking up mats of the green algae Cladophora from their rocky substrate in nearshore areas. Floating mats of Cladophora located in warm shallow water are ideal habitats for blue-green algae and bacteria growth. The presence of these floating mats contributes to taste and odor problems. Localized eutrophication problems in some nearshore areas may also contribute to taste and odor problems.

In summary, taste and odor problems are considered to be a locally impaired beneficial use in some areas. The causes, however, are poorly understood. Naturally occurring algae, eutrophic conditions, and zebra mussel controls may all be important contributing factors.

Localized beach closings due to occasional high bacteria levels are a problem in some areas and are being addressed by several Remedial Action Plans (RAPs). While some taste and odor problems have been observed, there are no restrictions on drinking water consumption.

In Ontario, beaches are closed when bacterial (E. coli) levels exceed 100 organisms/100mL. During recent years (1995 to 1997) beach closings have continued in heavily urbanized areas in the western part of the basin due to storm events, but are less frequent in the central and eastern regions. Examples of ongoing problems include the beaches of the Bay of Quinte, Toronto, Burlington, Hamilton, Niagara, Pt. Dalhouse, and St. Catherines. Upgrading stormwater controls through the installation of collection tanks so stormwater from Combined Sewer Overflows (CSOs) can be treated in Toronto and Hamilton should reduce beach closings in these areas.

Chemical contamination
Several epidemiologic investigations have been conducted on the association between water pollutants in the Great Lakes and the health of people in the Great Lakes basin. These studies have demonstrated increased tissue levels of toxic substances in these populations that may be associated with or potentially result in reproductive, developmental, behavioral, neurologic, endocrinologic, and immunologic effects.

It is extremely difficult to estimate critical pollutant loadings entering Lake Ontario via rivers, precipitation, sewage treatment plants, waste sites, agricultural areas, and other sources. The levels of contaminants entering the lake from these sources are constantly changing in response to many known and unknown factors. As a result, loadings data are often limited and rely on numerous assumptions. Although quantitative loadings information may be difficult to obtain, qualitative indicators provided by the environmental monitoring of water, sediment, and aquatic organisms can often provide sufficient information to identify those contaminant sources that need to be controlled. Improving the database on sources and loadings of critical pollutants is a high priority, as is determining effective ways to virtually eliminate these critical pollutants from Lake Ontario.

Preliminary estimates indicate that the volume of some contaminants leaving the lake, such as PCBs and DDT, may be greater than the amount coming in. One explanation for this may be that contaminants are slowly being released from sediments already present in the Lake Ontario system.

Estimates of atmospheric loadings of critical pollutants to Lake Ontario are developed by the International Atmospheric Deposition Network, who also provided estimates for the amounts of critical pollutants volatilizing to the atmosphere. Volatilization may be a significant process by which critical pollutants are leaving the Lake Ontario system. Estimating atmospheric deposition is difficult, and these estimates contain a significant degree of uncertainty.

The amounts of critical pollutants entering Lake Ontario via all of the Lake Ontario basin tributaries were based on representative point and non-point sources within each tributary’s watershed. Quantitative and qualitative monitoring techniques, as well as biological monitoring results, were used to estimate loadings or the relative presence or absence of critical pollutants within each of the 22 tributaries with the highest flow rate within the watershed.

Information on releases to the environment of critical pollutants and other contaminants is available to the public in publications developed and released on a regular basis by governmental agencies. For sources in the U.S., the annual Toxics Release Inventory (TRI) summarizes on an annual basis the emissions of approximately 650 pollutants from facilities nationwide. For sources in Canada, the National Pollutant Release Inventory (NPRI) provides information on the onsite releases to air, water, and land; on transfers offsite in waste; and on the three R’s (recover, reuse, and recycle) of 176 substances. The NPRI is the only legislated nationwide publicly accessible inventory of pollutant releases and transfers in Canada.

Based on the limited loadings data available, it appears that a significant load of critical pollutants to the lake originates outside the Lake Ontario basin. The upstream Great Lakes basin contributes the majority of the estimated loadings of PCBs (440 kg/year), DDT and its metabolites (96 kg/yr), and dieldrin (43 kg/year). Attention must also be focused on the Niagara River, since most of the mirex entering Lake Ontario originates in the Niagara River basin (1.8 kg/year) and it also contributes to the load of other critical pollutants into the lake. Atmospheric deposition is a source of critical pollutants and appears to be the largest known source of dioxins/furans, contributing approximately 5 grams per year.

Recreational water
Beaches | Critical contaminants

Beaches
Local beach closings along some of the more populated shorelines due to elevated levels of E. coli (or fecal coliform bacteria) are indicative of fecal contamination and the possible presence of enteric (intestinal) pathogens which can pose a potential health risk. Microbiological water quality indicators are used as surrogates for the presence of pathogenic organisms that may cause illness.

In Lake Ontario, a number of local beach closings occur due to microbial contaminants, primarily along the more populated shorelines. Exceedence of microbial standards and criteria typically occurs following a storm event when the treatment capacity of some sewage treatment plants can be exceeded. Given the localized nature of beach closings and their absence along much of the Lake Ontario shoreline, they are not considered a lakewide problem. The frequency of beach closings is expected to decrease as sewage treatment plants continue to improve and upgrade their systems. It should be noted that beaches may also be closed due to other factors such as storm events, excessive turbidity, or lack of funding.

Beach closings are restricted largely to shorelines near major metropolitan centers or the mouths of streams and rivers. These closings follow storm events when bacteria-rich surface water runoff is flushed into nearshore areas via streams, rivers, and combined sewer overflows (CSOs). In some instances beaches may be closed based on the potential for high bacteria levels to develop following storm and rain events. Beaches are also closed for aesthetic reasons, such as the presence of algal blooms, dead fish, or garbage. Given the localized nature of beach closings and their absence along much of the Lake Ontario shoreline, they are not a considered lakewide problem.

In Ontario, beaches are closed when bacterial (E. coli) levels exceed 100 organisms/100mL. During recent years (1995 to 1997), beach closings have continued in heavily urbanized areas in the western part of the basin due to storm events, but are less frequent in the central and eastern regions. Examples of areas with ongoing problems include the beaches of the Bay of Quinte, Toronto, Burlington, Hamilton, Niagara, Pt. Dalhouse, and St. Catherines. Upgrading stormwater controls through the installation of collection tanks so stormwater from CSOs can be treated in Toronto and Hamilton should reduce beach closings in these areas.

The only U.S. beach on Lake Ontario with recent closings is Ontario Beach within the Rochester Embayment Area of Concern (AOC). These closings have been posted due to rain events, storm runoff, excessive algae, waves greater than four feet, or visibility less than one-half meter. Ontario Beach is routinely closed as a precaution during storm and rain events because these conditions have the potential to cause high bacteria levels along the beach shore. Ontario Beach summer fecal coliform levels have been well below the state’s action level of 200 fecal coliforms/100mL. The implementation of a combined sewer overflow abatement program resulted in significant decreases in fecal coliform levels in the Genesee River and adjacent shoreline areas. Actions are also underway to address stormwater problems that impact other areas of the Rochester Embayment.

Fish consumption
Critical contaminants | Reducing exposure
Specific fish advisories: New York | Ontario

New York
New York Fish Consumption Advisories
Health Advisory: Chemicals in Sport fish and Game
A Family's Guide to Eating Fish from the Lake Erie Basin
Health Advisory for Fish Consumption
Advisory for Specific Waters

Ontario
Eating Ontario Sport Fish
A Family's Guide to Eating Fish from the Lake Erie Basin
Mercury in Fish: A Special Advisory (PDF)
Mercury and Fish Consumption
Information on mercury levels in fish

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