Cootes Paradise Marsh Aquatic System Reset; Post July Floods & Recovery

By Tys Theijsmeijer, Senior Director of Ecosystem Stewardship Programs and Policy

A record setting July locally for precipitation has changed circumstances on how to mitigate Climate Change and restore water locals. The rains of July lead to floods, large scale erosion, washouts, and substantial sewer spills. With much of that water passing through Cootes Paradise Marshes, it essentially wiped out the existing aquatic ecosystem that had developed. Peak flood flows through Cootes Paradise from the combined 17 creeks and overall 280km² of upstream watershed were upwards of 40m³/s. As an example of sewer overflow issues, the Royal Stroud Combined Sewers Spill holding tank, along Chedoke Creek, overflowed for 14.5 hours & 20million liters for just one of the storm event, an example of one of many July sewage spills.

Post storm, nature is again working on healing itself.  Step one of the aquatic food webs rebuild is phytoplankton growth (single celled algae – plants), that stains the water green as it explodes in population in the raw waters post storm. The excess amount of this algae is fueled by the excessive nutrients flowing in and so the algae density turns the water almost to the colour of Lime Kool-Aid at the peak of its growth. Ending this excess algae problem is the long-standing challenge that all partners in of the Hamilton Harbour Remedial Action Plan are working towards.

The marsh is a fragile aquatic environment hanging in the balance between its past degradation and its current recovery. Pre-storm, in June this year, Cootes Paradise Marsh had managed to cross the threshold of restoration and regenerate into something resembling a real marsh with a diversity of aquatic plants and a burgeoning population of water lilies. A situation dreamed of by many people since the system collapsed in the 1940s. In 2024 it was finally occurring. This came to a full stop on July 15 as the string of localized rain events passed through the region. That Monday morning, I sat in my office collecting and coordinating the damage and repairs information that would already be needed following the previous week’s rain event from the remnants of hurricane Beryl when it all changed. At 11 a.m. rain started falling at an intensity and volume I had never seen before. Even the Arboretum filled with water and became a temporary lake. The ensuing runoff across the region changed our collective perception of what can now occur and what the lands can withstand.

On a more positive note, a shadow of the marsh recovery remains in the sheltered Westdale Inlet area of Cootes Paradise, on the west side of Princess Point. At the head of this inlet is a long-standing spill point for sewage from the sewer system that wraps around the west of Cootes Paradise and up to Waterdown. The massive rebuild of the control system in the area in 2023 seems to have legitimately solved this site’s challenges based on the aquatic system that still remains within the inlet after this past July’s rains. The dirty work of recovery continues and a key piece of the puzzle is up for community input and discussion, the draft City of Hamilton Watershed Action Plan – Aug 20 2024. The Westdale Inlet area remains as result of the broader sewer system projects.