There were two reports of fish kills in the O'Leary area of P.E.I. on the weekend.
Hundreds of dead fish were found both in the Trout River and Big Pierre Jacques River.
Kim Devine of the provincial Department of Environment, Energy and Forestry said investigation enforcement and emergency response staff were on site at Trout River collecting samples Saturday morning.
Crews investigated the fish kill at Big Pierre Jacques River Sunday morning.
Department staff collected soil, water and fish for analysis.
Thousands of dead fish
Dale Cameron, part of a local watershed group, has spent the last three days leading a crew of a dozen volunteers cleaning up the dead fish.
"We get a very small percentage. If we've got hundreds of fish here, there's probably thousands," he said Monday. "We'd like to spend our energies on conservation and enhancement, not picking up dead fish."
Roseanne MacFarlane, a provincial biologist, is part of the team looking into the deaths.
"We certainly cannot point to any cause on this fish kill yet, because we're still undergoing the investigation," she said. "We're looking at all angles. We'll certainly look at heavy rainfalls and possible runoff as one potential source."
The province will introduce trout to the river to rebuild the population, but it will take years to recover.