'Combination of factors' likely led to fish kill in Morell River, says P.E.I. fisheries biologist

The death tally keeps rising as officials continue to investigate the fish kill discovered late last week in eastern P.E.I.'s Morell River.

Environment Department staff and conservation officers have found more than 200 dead fish in the river's east branch so far. That includes more than 100 brook trout, the game fish that makes it a popular spot among sport fishers.

Provincial fisheries biologist Rosie MacFarlane was called to the site shortly after crews removing a culvert blockage in the area spotted some dead fish Friday morning.

"Water level was up higher because the blockage in the culvert had just been taken out," she said. 

"You could see as the water level dropped some fish moving down from upstream, some dead fish were visible. So we put a canoe in here, we went upstream and we picked up a number of dead fish and we also went below. Just in an area of about 500 metres, we picked up 100 dead fish."

Officials have taken water and fish samples for analysis. They've also done some water testing, which MacFarlane said showed dissolved oxygen levels were "far below" what's needed to sustain fish in that section of the river.

Multiple factors likely behind event

While the investigation is still ongoing, she said that a deadly combination of factors was likely behind the event.

"We've known for many years that this is the warmest section of the Morell River," she said. 

"We did have an extended heat wave this year and things got very warm. And I think there might have been a combination of factors, with the water being higher than normal with the blockage in that culvert, and then that massive rainfall that we would've had about a week ago that might have flushed poor-quality water downstream where trout are holding."

The levels of oxygen in a stream drop as the water gets warmer. 

MacFarlane said temperatures in this section of the river could get as high as the mid-20s between July and August. That's because it's in a flat, open area with marshy terrain where the water is darker and therefore absorbs more heat.

'A blow'

The fish kill comes after years of efforts to improve the water quality in this branch of the Morell River, including the removal of an old millpond dam that had been slowing the flow of water.

MacFarlane said the branch is the river's most productive for trout, and it's where the province gets its brood stock in the fall.

"It is a blow, because many of the fish that we were picking up are larger trout in the 18- to 22-inch range, three or four pounds," she said. "They hold here throughout the summer, fall months and then they spawn."

On Monday, crews were installing oxygen monitors across the river that will read levels every hour.

The east branch will be closed for sport fishing for the rest of the season, though MacFarlane said it is not a popular section of the river for anglers during the summer because they prefer cooler spots.

In the meantime, the province said rehabilitation efforts will focus on stocking for years to come, including the release of 3,000 brook trout fingerlings in the fall.