At the edge of Cootes Paradise, a narrow structure performs two jobs at once. Its grates keep large common carp out of the marsh. Its operating lifts allow staff to handle, count and move larger native fish travelling between Lake Ontario and spawning habitat.
In 2025, Royal Botanical Gardens staff handled 26,503 fish there: 11,562 large fish and 14,941 smaller fish caught incidentally. More than 100 salmon were also observed spawning upstream in Spencer Creek, but those fish were not included in the total because the structure is opened during the fall run.
- 26,503 fish handled at the Fishway
- White sucker became the most abundant recorded species for the first time
- Bowfin and white sucker increased
- Common carp, goldfish, rudd and brown bullhead declined
- More than 100 salmon were observed spawning upstream
A good number is not the same as a healthy marsh
The restoration goal is not simply to maximize the number of fish crossing a checkpoint. It is to rebuild a community dominated by native species while keeping destructive common carp close to zero.
RBG’s report describes a striking contrast. Grindstone Marsh was dominated by native species such as sunfish. Cootes Paradise remained dominated by introduced Eurasian species, particularly goldfish. The major dividing line was water quality.
During summer, decomposition and excess nutrients can drive oxygen close to zero. Goldfish tolerate those conditions unusually well. Many native species do not. That means an ecosystem can contain millions of young fish and still be selecting for the wrong community.
The brief return of a marsh
For a period in June and July 2025, aquatic plants spread across Cootes Paradise from end to end for the first time since the 1930s. Summer heat later brought rafts of algae, but RBG expects many plants to survive and expand.
That short-lived transformation explains why the Fishway story is bigger than a count. The structure can manage carp and measure migration. It cannot solve sewage inputs, nutrient loading or low oxygen on its own. Recovery depends on what happens throughout the watershed.