A combination of factors – including lack of precipitation and low water flow – caused large fish kills in the Rigaud River near St-Eugène in early September, a spokesperson said. from the Ontario Ministry of Environment, Conservation and Parks (ME).
“After careful consideration, the ministry determined that the fish deaths were triggered by a combination of factors, including a long period without significant precipitation, pre-existing water levels, slow water flows, low levels of water. dissolved oxygen and high water levels. river temperature at that time, ”wrote Michael Seguin, area supervisor for MOE’s Cornwall regional office, in an email to The Review on Monday, October 25.
Christopher Brown, who has lived on his waterfront property on the river near St-Eugene for over 30 years, contacted the ministry’s Action Center on September 2 – the day after he first noticed an odor. “Sewer” emitted by the river. On September 4, he spotted the first of a large number of fish that floated to the surface over the following days.
Representatives of the Ministry of the Environment have visited the site on several occasions, taking water samples and sending them for analysis.
“Regarding the sampling results, the ministry observed that the quality of the bottom water in the Rigaud River is strongly influenced by agricultural land uses in the watershed and that the nutrients and solids in it. suspension related to agriculture are normally high, ”Seguin wrote. “The ministry recorded high temperatures and low levels of dissolved oxygen in the Rigaud River.
“Environment Canada’s river gauge located at the Chemin Duplantie bridge recorded low flows in late August and early September.
The ministry report also noted that dead fish were observed along the entire stretch of the Rigaud River between Duplantie Road and the provincial border between Ontario and Quebec. An assessment of private property in the area revealed no observable contamination released directly or indirectly into the Rigaud River when the fish died.
“The dark water reported to the ministry by area residents and observed by ministry staff can be attributed to suspended solids sedimentation in the absence of significant rainfall events in August and low river flows in August. over time, ”Seguin wrote, noting that dark and clear water was also observed flowing from tributaries along the Rigaud River.
Between the Duplantie Road bridge and the Ontario-Quebec border, the surface water was dark, free from suspended matter and rich in chlorides (salt). The presence of high levels of chlorides in the region is not unusual, Seguin said, since natural and high levels are known to be present in the region’s groundwater in the former basin of the ancient Champlain Sea. . However, the presence of high chlorides in surface waters is not characteristic compared to the typical quality of surface waters in the region.
In his email to The Review, the area supervisor for MOE’s Cornwall regional office also addressed the strong odors reported by several residents near the river.
“Due to the low flow rates and the suspended solids deposited, the source of the odors reported as ‘sewage-like’ can likely be attributed to the standing water conditions at the time,” Seguin wrote. “The smell is not due to the actual sewage.”
Seguin said the ministry would continue to work to identify the source (s) of the high chlorides in the Rigaud River, but the chloride concentrations found at the time were not present at levels high enough to be a contributing cause of the death of fish.
Contacted by The Review on Monday, Brown said he was not happy with the report and that it is raising broader questions about the contamination of the Rigaud River from farming operations. He suggested that the MOE may need to review the contamination levels allowed by farming operations, in order to reduce stress on fish in the river during periods of low rainfall.