Published on Friday, 8th Jun, 2018 at 12:22pm
E. coli is short for Escherichia Coli, a type of gram-negative bacteria found in the feces (poop) of mammals and birds. During periods of high rainfall, E. coli finds its way into the lake from surface runoff and overflow from storm sewers and older combined sewers. Animals, especially dogs and birds (geese, swans, seagulls and ducks) can also be significant contributors to E. coli contamination. Runoff from beaches, parking lots, roads, and yards carries animal waste to the lake.
Most E. coli strains are harmless, but virulent strains can cause gastroenteritis, urinary tract infections, and other illnesses. Very young children, the elderly and immunocompromised individuals are more susceptible to developing serious illness from E. coli, but even healthy people can be sickened. In May 2000, 7 people died and 2,300 became ill in Walkerton when the town's water supply was contaminated with E. coli. The contamination was caused by runoff from a feed lot leaking into a town well.
At the beach, E. coli is typically ingested by swallowing water while swimming, a particular hazard with children. The incubation period is typically 3 to 4 days after exposure, but may be as little as 1 day, or as long as 10 days.
While most E. coli in water may not be directly harmful, it is an 'indicator microorganism' that other pathogens may be present. The Ontario Ministry of Environment and Climate Change sets the standard for beach water quality at 100 E. coli bacteria per 100 millilitres of water. Swimming in water with E. coli levels greater than the provincial standard exposes the bather to increased risk of infections.
Each year during the summer, between the first week of June and Labour Day, the City of Toronto Department of Public Health performs daily water sampling and E. coli testing at all Toronto public beaches and publishes the results online at SwimSafe. The Toronto Lifeguard Service also flies red flags at lifeguard towers and stations when E. coli exceeds 100 per 100ml, to warn beachgoers to avoid swimming.
Woodbine Beach and Kew-Balmy Beach are both recognized as Blue Flag beaches, an international program that sets stringent standards for E. coli and other water-borne contamination, among other criteria. The program is run in Canada by Environmental Defence.
For this article, we collected the City's E. coli test results for every testing day from 2007 thru 2017. Because E. coli levels are influenced by rainfall and temperature, we also collected climate data from Environment Canada for each day, including total rainfall, wind, and high, low and mean temperatures. We chose weather data from Toronto Island airport, the nearest station with data covering the entire 11-year period. Where data was missing or incomplete, we used data from Toronto Pearson Airport.
For Woodbine Beach, the number of beach closure days due to high E. coli has dropped from an average of 7.25 days per year (2007-2010) to just 3 days per year (2012-2017), a drop of 60%. One year, 2011, had no closures at all. Based on an average 92 days per season between June 6 and Labour Day, Woodbine Beach is safe for swimming 96.75% of the time
Figures for Kew-Balmy Beach show a similar trend, although overall the number of unsafe days is still more than double than of Woodbine Beach. The number of closure days, on average, has dropped from 13.4 days per year (2007-2011) to 7.3 days per year today (2012-2017). This means Kew-Balmy is safe to swim about 92% of the time during the summer, or unsafe 8% of the time.
For some historical background, in 2001 Woodbine Beach was closed 16% of the time, Kew Beach 17% cent, and Balmy Beach 28%.
Temperature and rainfall play a major role in E. coli contamination. Dry years with little rainfall tend to reduce contamination, while wetter years generally tend to increase E. coli. More significantly, as the lake warms up throughout the summer it provides a better home for bacteria; nearly half of beach closure days occur in August, when the lake temperature reaches its peak.
The data clearly indicates that the overall decrease in E. coli contamination is both significant and sustained, although the high number of closures on Kew-Balmy (8% of all summer days) is still far from ideal. The fact that Kew-Balmy experiences more contamination than Woodbine is almost certainly due to geography; Kew-Balmy is bordered to the north by dense development, with a steep slope north of Queen St that funnels runoff down to the lake. It's not unusual after a heavy rain for storm sewers to overflow and flood the foot of Glen Manor Dr. and other streets bordering Kew Beach. The dog park at Leuty probably doesn't help.
Woodbine Beach, by comparison, is more distant from areas of dense development, with parkland to the North and broad, flat swaths of beach to absorb runoff. Despite its proximity to Ashbridges Bay, it is consistently the safest swimming beach in Toronto.
The bigger question is how to account for the dramatic overall decrease, especially since 2012. As we noted earlier weather is a factor, with warm, wet weather favoring higher E. coli counts. This was certainly true before 2011, however the relationship has become less pronounced in recent years. 2013 was the wettest summer in the 11-year series, yet beach closures didn't spike. So while climate plays a role, it's not the whole story.
Starting in the late 1980's, the City of Toronto and the Toronto and Region Conservation Authority began a series infrastructure upgrades aimed specifically at controlling stormwater runoff in order to reduce pollution in the lake. This was a major problem at the time, because many of the sewers are 'combined sewers'; raw sewage and stormwater draining into the same pipe. Whenever the storm sewers overflowed from heavy rains, they carried raw sewage along with them into the lake.
In 1995 the City installed the Maclean Avenue detention tank (pictured below), an 8000 m3 underground tank designed to temporarily hold stormwater and combined sewer overflow for up to 8 hours after a storm, rather than dumping it directly into the lake. They quickly realized that it was too small. A second tank was later added at the foot of Kenilworth Ave .
Govt. of Ontario
In 2003 Toronto City Council adopted the Wet Weather Flow Master Plan, a 25-year program of stormwater and combined sewer management, downspout disconnection, and other flooding control measures. With about $485 already million already invested into the program, the City has been ramping up funding. The 10-year capital budget for Toronto Water (2017-2026) includes $3 billion for stormwater management, basement flooding remediation, and wet weather flow management. The City plans to invest a total of $6 billion in infrastructure-renewal funding over the next decade. The Ashbridges Bay Plant, which is included in the Toronto Water capital budget, will also be receiving numerous upgrades aimed at increasing capacity, reducing bypasses, and reducing outdoor odor from the plant. The plant received a four-year, $58 million upgrade between 2011 and 2014.
Woodbine and Kew-Balmy Beaches are cleaner than they were a decade ago, at least as far as bacterial contamination is concerned. The City and TRCA's efforts are showing positive results, and further improvements are likely over the coming years as new infrastructure upgrades come on-stream. However, there are other environmental threats to Lake Ontario and the Beach, notably plastics and microbeads. Continued development and increasing density will put the Beaches under ever greater environmental pressure. Nine-million people rely on the lake for drinking water. And the massive flooding of 2017 caused severe damage to the Beaches shoreline and habitat that will probably take a decade to repair.
Nonetheless, we plan to do a lot of swimming this summer.