The Ups and Downs of Lake Ontario – And the Marsh Drains Away Again

By Tys Theysmeyer, Head of Natural Lands, Royal Botanical Gardens.

Paddling in Cootes Paradise Marsh will be a challenge throughout this fall as a dry year has led to below average and declining Lake Ontario water levels. Lake levels will continue to decline rapidly without rain, and I expect at least ½ of Cootes Paradise Marsh to be without water during the fall, with the remainder very shallow.

Currently large mudflats in the creek deltas are already appearing, a result of lake levels 20cm (8in.) below average.  The deep end of Cootes Paradise currently averages 70cm (28in). Downstream of the lake, the Board of Control states “Lake St. Lawrence water levels are record low for this time of year”.

While paddling in Cootes Paradise will be tough, the regeneration of the reeds will receive a boost with these conditions and continue recovery. Last year was a fantastic regeneration of missing reeds after several years of loss regenerating many missing hectares of habitat. However, 2022’s dry conditions concentrated inflowing pollutants, and the marsh plant life was again impacted by poor spring and summer water quality, with about a 1/4 of 2021’s plant regeneration lost.

Through the remainder of the year, the growing reeds on the wet mudflats will enjoy a boost helping the regeneration of last years surviving plants in ideal growing conditions.  The noteworthy reeds growing include Cattails, Giant Bur-reed, and several bulrush species including Hardstem, River, American and Softstem Bulrush.

Lake Ontario is expected to recover water levels again this winter once evaporation eases, because inflowing Lake Erie continues to be above average (although declining), sending Lake Ontario ample water to refill.