There's been a lot of recent back and forth in multiple threads, passim, between Swim Team (the water is fine) and the Icky Poopy brigade (the water is icky and poopy).
So I went back and looked at recent actual data from three sources:
CU (Carleton University): Collected by Dr. Banu Örmeci and team from Carleton University in the summer of 2025
https://carleton.ca/ormeci/rideau-river-water-quality-testing/
RK (River Keeper): Collected by Ottawa River Keeper, 2025-present
https://ottawa-riverkeeper-open-data-ork-so.hub.arcgis.com/datasets/afe7fde714bf460e88cf139483bf0d68/explore
Ott(awa): Collected by Ottawa Public Health, 2025-present
https://www.ottawapublichealth.ca/en/public-health-services/beach-water-quality-results.aspx
I really only looked in detail at the Ottawa and Rideau River testing, but there is similar data available for other sites, such as Dow's Lake and Lac Beauchamp. If anyone knows how to get the same sort of data for Lac Leamy, Gatineau Park lakes, and Gatineau city municipal beaches, drop it in the replies.
For each testing site, I calculated the following:
- Median: By way of an overall E. coli "score", this is the median of all the test results for that site over the time period. The unit is E. coli thingies per 100 ml. (They need to come up with a snappy name for this unit.)
- Passrate: Percentage of test results at that site which were under the 200 Ontario/Ottawa standard
- Euro Passrate: Percentage of test results at that site which were under the 500 European union standard (for sea water), for funsies.
I then smooshed the results from all the reporting programs together. (There are a bunch of actual, not-crude scientific reasons to not smoosh these separate data sets, but it's the data we have, so that's that.)
(Note that sites indicated with an asterisk* in the graphics to follow have small numbers of reported samples.)
OTTAWA RIVER - 243 samples
Overall, the Ottawa River testing locations had median E. Coli results well within the 200 standard. Petrie River, and all testing sites above Petrie, had medians below 100. Petrie East (or "Bay") and Petrie "Picnic" had medians above the threshold, with the caution that limited testing has been done at the River Keeper "Picnic" site.
Setting aside the Petries, the remainder of the Ottawa River reporting sites passed the Ontario limit 91% of the time, and the Euro limit 96% of the time.
On the available data, there is penetrating insight into the obvious hypothesis that the water quality degrades as it passes through the urban area:
- Upper Rural: The four River Keeper testing locations above Aylmer had medians between 2 and 19, and passed 93% of the time.
- Upper Urban: The four municipal beaches above the Chaudière Falls had medians between 28 and 84, and passed 85% of the time.
- Central Urban: The four River Keeper monitored sites (NCC swim docks plus the Rowing Club) had medians between 19 and 71, and passed 95% of the time.
- Petries: The collective Petrie Island testing sites had medians between 72 and 436, and passed 54% of the time.
Observations:
- The Upper Urban beach sites scored a little worse as a group than the Central Urban sites. This is consistent with the idea that the episodic lower water quality at places like Westboro and Moussette is caused by localized stormwater drainage, bird soiling, and human activities at and near those sites, as has been hypothesized for decades. But this is also based on a smaller comparative data set for the Hull and East Wharf docks; it will be interesting to keep an eye on this as more data comes in over time.
- The distribution of bad numbers for the Petrie sites are heavily skewed. Petrie River, in the main flow of the River, tests much better than the Petrie East/Bay/Picnic sampling sites (Median 166 vs. 25; Passrate 69% vs. 37%). In fact, the Petrie River testing has a slightly lower Median than Parc Moussette well upstream, but a somewhat worse Passrate. If you have lagging concerns about Petrie, stick to the River side and enjoy the current.
RIDEAU RIVER - 116 samples
Overall, the Rideau River testing locations had median E. Coli results well within the 200 standard. Almost every testing site from Manotick down to Dutchie's had a median below 100. Bordeleau and Windsor were both above 100 but below 200. The one test that the Carleton team did at Strathcona Park was elevated (277), but as Dr. Örmeci's report notes, there was also abundant bird activity there at that time (and there almost always is in those shallow rapids, which is like a city, for birds.)
The Rideau River reporting sites passed the Ontario limit 81% of the time, and the Euro limit 95% of the time.
Again, on the available data, there is penetrating insight into the obvious notion that the water quality is prone to get worse as it passes through the urban area. Generally speaking, the further upstream the testing site, the better the results, bearing in mind that the number of samples for some sites is still quite small.
Observations:
- The City of Ottawa's tests at Mooney's last summer had a higher (but still fine) median, and higher "failure" rate, than three Carleton sites, including two downstream, and higher than River Keeper results in the same general location.
- Carleton's Windsor site was a big outlier to the general "downstream" trend that the data shows overall, with higher Medians than other site downstream apart from the single-sample Strathcona results. However Windsor still passed more often than Mooney's. While Windsor was almost always the most elevated sample on the lower Rideau, the City testing showed Mooney's with even higher levels, despite being upstream. That is: When Mooney's quality gets worse, it gets worse-er, which again suggests some idiosyncratic local impact, but also something that is rapidly diluted.
OVERALL
- The Ottawa and Rideau River water-quality testing last year and so far this year, shows that "the water" met the Ontario standard 80% of the time.
- The Upper Ottawa (i.e., Petries excluded) met the standard 91% of the time, and the Rideau, 81%.
- If we applied the European sea water standard of 500, the water quality would have passed 92% of the time; 96% on the Upper Ottawa 96% and Rideau 95%
- If we applied the European fresh water standard of 1000 (which is the threshold Paris uses for the Seine), the beaches would almost never be closed. It wasn't even worth the effort of applying the European fresh-water standard to the urban Ottawa and Rideau test results.
- Even if we applied the very strict Toronto standard of 100 for its Lake Ontario beaches, the Upper Ottawa passes 83% of the time, and the Rideau 70%.
- The Ottawa River above Aylmer, as it is about to enter the urban area, is cleaner than Lake Ontario beaches in Toronto. The Hull docks, Dow's Lake (!), Britannia Beach, River House, Westboro Beach, Parc Moussette, and Mooney's Bay would all pass the Toronto standard about as often as Toronto's lakefront beaches do.
- This week's OPH samples were not included in the above math-ing; if they were, the Median and Passrate for the Ottawa Public Health sites would tick slightly higher.
- The fresh Ottawa Public Health data has Petrie East at 328, but the other four Ottawa city beaches are all under 100. (Britannia 18, Westboro 30, Petrie River 80, Mooney's 39).
