Using the Open Data Ottawa website, I acquired the statistics on bacteria levels at Ottawa beaches for the last three summers. There are 5 beaches monitored by the city: Brittania, Mooneys Bay, Westboro, Petrie Island River beach and Petrie Island East Bay. They are tested every day by Ottawa public health staff for E. Coli levels
E. Coli is known as an “indicator” bacteria, meaning that their presence is an indicator of fecal pollution and that other, more harmful pathogens are likely present as well.
If there are over 100 E. Coli per 100 mL of water, an advisory will be put out the next day to warn the public. If there are over 200 E. Coli per 100 mL, or more than 100 for two consecutive days, a no swimming advisory will be issued.
An advisory will also be issued after a heavy rainfall (20mm or more) since it can wash many contaminants into the river. On top of that, sewage overflows from sewers carrying both storm water and untreated sewage can also occur during a heavy rainfall, affecting all beaches downstream.
Here is a map of the combined (storm water+sewage) sewer overflows in Ottawa. This is where potential overflow caused by heavy rain will enter the river.
This is important to note because the beaches at Petrie Island are the only ones downstream of downtown Ottawa/Gatineau.
I put the data into excel and sorted it to show the number of days over 100 E. Coli and the number of days over 200 for each year. Then I graphed the data using the website DataHero.
I determined that the overall amount of no swim advisories were way down at all beaches this summer, with Petrie Island river beach, Westboro and Brittania only having 7.
For comparison, in the summer of 2014, Petrie Island river beach had 16.
I spoke with with representatives from Ottawa Riverkeeper and Ottawa Public Health, to discuss possible reasons for this decrease in no swim advisories. They speculated that the work done by the city on the combined storm water and sewage systems downtown could be partially responsible. They said a particularly dry summer could also be a factor. Additional engineering controls by the city to deter birds, such as stringing wires and even using drones to scare them off could also have contributed.
Brittania beach has historically been one of the cleanest beaches and the representative from Ottawa Public Health explained that the large pier at the beach deflects some contamination away from the shore. There are also wires used to deter birds. It is also the farthest beach upstream from the Ottawa/Gatineau downtown, which is also beneficial.
In conclusion, bacteria levels in the Ottawa river are caused by many different environmental factors including rainfall, positioning on the river, and wildlife. No swim advisories are down significantly this year, and one of the reasons could potentially be the work done by the city on its combined storm water and sewage systems.
Sources:
Data set:http://data.ottawa.ca/dataset/beach-water-sampling-data/resource/ab85fe8e-98c4-4388-9dc3-2839890f637d
http://www.petrieisland.org/water-quality-archives
http://www.ottawariverkeeper.ca/beach-closures/
http://app07.ottawa.ca/blogs/physicians/2015/07/23/is-it-is-safe-to-swim-at-ottawas-beaches/