Dead fish were discovered on a two kilometre section of the east branch of the Montrose River on Tuesday.
The incident was reported by the Huntley-Montrose-Kildare Watershed Association.
Heavy rain fell on P.E.I. on Saturday and Sunday.
Environment officials have been on site collecting samples of fish, water and soil for analysis.
Officials are on site today continuing their investigation.


Boy people sure are fast to jump all over EVERY farmer without knowing the facts. Funny thing is when you sit down to eat a meal do you think of the farmer that worked so hard to provide that for you? And what about the ones who follow all the rules and regulations you seem to always put them in the same class as the ones that don't.Do you really think that these farmers want to spend their time and money on chemicals if it was not necessary? Be careful what you wish for, no farmers means no food.