April 10, 2015 – The cold, harsh temperatures this winter caused extensive ice coverage on local lakes and ponds in the Credit River watershed.  Prolonged cold periods in January and February contributed to thicker ice, which affects oxygen levels in the water and result is higher than normal fish mortality in the spring. This is a natural phenomenon known as winter die-off or “winterkill”.

“Winterkill happens naturally and is common in shallow lakes and ponds. When ponds and lakes freeze over with thick ice and snow the water becomes separated from air. It reduces the amount of sunlight available to aquatic plants,” said Jon Clayton, Aquatic Biologist for CVC.  “This limits the amount of oxygen available for fish. Without enough oxygen, fish die.”

Ontario experienced one of the coldest Februaries on record this year, which resulted in more ice coverage on our lakes and ponds. Our Great Lakes saw approximately 86 per cent coverage this winter, compared to 61 per cent last year. Once spring temperatures normalize and the ice begins to melt, fish mortalities become obvious.

Fish mortalities are usually reported in places where ice initially melts. The lakes and ponds at Island Lake Conservation Area and Ken Whillans Resource Management Area are susceptible to winterkill events. Please notify Credit Valley Conservation staff if you see results of a large winter die-off.

CVC staff will monitor fish species that experience winterkill and the extent of any die-offs.

If you have any questions or concerns please contact CVC Aquatic Biologist, Jon Clayton (905) 670-1615 ext. 502 or [email protected].

Conservation authorities are a provincial/municipal partnership. For 60 years, Credit Valley Conservation has worked with its partners to support a thriving environment that protects, connects and sustains us. Credit Valley Conservation gratefully acknowledges financial support from our member municipalities for facilities, programs and services: the Regions of Peel and Halton; the Cities of Mississauga and Brampton; the Towns of Caledon, Erin, Halton Hills, Mono, Oakville and Orangeville; and the Townships of Amaranth and East Garafraxa. CVC is a member of Conservation Ontario.

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Media Contact:
Jamie Williams
Marketing and Communications Specialist
Credit Valley Conservation
905-670-1615, ext.285
[email protected]

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