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Low Waters and Ecological Implications

November 10, 2022

By Tys Theysmeyer, Head of Natural Areas, Royal Botanical Gardens

A truly dry summer and fall has led to challenging conditions for fish and wildlife.  Overwintering amphibians and turtles have few pond options currently, fall spawning salmon and trout can’t access creek spawning sites in the local creeks and fish generally must seek the deeper water of Burlington Bay. On the positive side coastal marsh plants such as cattails in Cootes Paradise (plants lost during the Chedoke spill) have had ideal conditions to regenerate in Cootes Paradise and much of the plant loss is now healed.

Grindstone Creek delta with low water
Grindstone Creek Delta, October 2022
View from a distance of the low water at the Spencer Creek Delta
Spencer Creek Delta, October 2022

Despite an ongoing drought, Lake Ontario water levels have held steady about 20 cm below average, while many creeks have no flow at all. Holding the lake stable has occurred by a reduction of the lake flow down the St. Lawrence River – controlled by the Moses Saunders dam at Cornwall. Locally the largest of the creeks, Spencer and Grindstone Creeks, measured flows of zero water on the water survey of Canada Gauges in Dundas and Aldershot areas respectively in October. A site visit to these creeks showed that a dribble of water was flowing between the rocks. Since that time a small amount of rain, combined with the fall shut down of evapotranspiration by plants has restored a small base flow to these creeks, but barely enough for a large fish like a salmon to use, and with most of the small creeks still without flow.

More problematically for the salmon run from the lake is that the low water channel at the creek mouths is annually filled with eroded watershed sediment creating a physical barrier for these large fish, currently with only 1 inch of water dribbling across the mudflats exposed by low lake water levels. Each spring these channels are recut and restored with the freshet of snow melt. The source of this sediment is urban storm water runoff erosion tearing apart the many small escarpment streams and sending it downstream to Cootes Paradise and Grindstone Creek Marsh.

The water volume fluctuations are at new extremes, just 3 years ago Lake Ontario set a new high-water mark (5ft higher than current water levels), and last fall creeks were flowing at almost record levels as rainstorm after rainstorm trounced the landscape. The Cootes Paradise Fishway/carp barrier was underwater 3 years ago, while this fall the marsh is essentially drained, with a current maximum depth of 14 inches and most of it without water. Since fish would become trapped as the water dries up and freezes, this fall the carp barrier has generally been left open. This has also had the benefit of letting left over carp from the 2019 record high water, swim back out to the harbour on their own.

In support of the dry conditions, a Level 2 Low Water Condition was declared for the entire Hamilton Conservation Authority (HCA) watershed on October 20. HCA also issued a letter to Permit to Take Water holders regarding Level 2 Low Water Conditions. The Level 2 Low Water Condition declaration included a request that water users of surface and groundwater sources voluntarily reduce their normal water use by 20%.

Water will of course ultimately return to the area and life will be renewed but the swings in weather amplified by a changing climate are evident.

Additional Resources

lower water through the Grindstone Creek
Low water channel of Grindstone Creek

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