A recent article in the renowned National Geographic suggested that non point-source pollution, carried by stormwater, accounts for approximately 80% of the degradation in North America's freshwater lakes and streams. The article drew attention to a problem often overlooked by the general public; while point-sources attract headlines and attention, stormwater runoff pollution draws mostly indifference.

Many recreational lakes face the threat of oil contamination from stormwater runoff. Photo - T. Davey

There are three reasons for the low profile for non point-source pollution.

First, the effect of stormwater on the environment is cumulative, and not immediately apparent. The impact of petroleum products spilled into streams is felt almost at once. Trickle small quantities of pollutants through the storm sewer system and it may take years to become evident, especially with groundwater contamination.

Toronto's Don River is an example of the cumulative effect of non point-source pollution. The Don, which runs through a heavily urbanized area of the city, has become a symbol of pollution to many Toronto-area residents. There are stories of researchers developing skin rashes from contact with the river during the 1980s.

Yet less than a century ago fishermen pulled healthy fish from the river for local markets. It took several decades of neglect for the Don to reach such high levels of pollution.

In 1993 and 1994, Toronto averaged about 400 reported petroleum spills annually. Many of these spills were carried through storm sewer systems directly to streams flowing into Lake Ontario, eliminating any chance to prevent their entry or treat the runoff. These are only reported incidents of petroleum spills. How many more occur annually and go unreported? One hundred? Two hundred? One thousand? Each year in the US, 133 million US gallons of motor oil are lost or unaccounted for.

The oil dropped daily on North American parking lots would surely rival many of the headline grabbing tanker disasters.

The problem is complicated because many citizens assume storm sewer systems lead to treatment plants, when that is not the case at all. Stormwater equally impacts environmental health as fumes do from factory smokestacks. The fumes are visible, the storm sewer flow isn't.

When you talk stormwater quality measures, most people think you are primarily concerned about protecting fish, frogs, and other aquatic life. But aquatic life is only one important reason for removing pollutants from stormwater; more importantly they are a prime measure of degraded water quality for human consumption.

Degraded water quality affects recreational uses of water resources. Fish disappear and a study in California found that people who swam near storm drain outfalls were 50% more likely to suffer fever and vomiting than those who kept their distance.

Degraded water quality also has a long-term impact on supplies of drinking water. Contaminated potable water sources require more complex, and expensive treatment facilities. Economic impacts are inevitable. Sports fishing disappears, taking tourist dollars with it and dredging costs for harbours and waterways escalate. Disposing of oil contaminated dredgings inevitably presents more expensive problems to solve for the future.

Unquestionably stormwater contamination directly affects our water quality. Unfortunately, most attention on water pollution problems has been focused on point-sources such as sanitary sewage and industrial discharge.

Raised awareness of problems associated with non point-source pollution will lead to a sense of stewardship for our freshwater and groundwater systems.