2025 Fish Monitoring Results Tell Story of Resilience

Taryn Smit and Rachel Saunders collecting aquatic monitoring data

In 2025, our aquatic biology team visited 74 locations across the Upper Thames River watershed to check on the fish that call our creeks and rivers home. These locations ranged from farm crossings to city parks, familiar bridges in neighbourhoods, and school routes. Together, they give us a good picture of how the watershed is functioning and how well it continues to support aquatic life.

2025 results show a system that is holding its own. The fish community remains varied and widespread, and many of the species we rely on as indicators of stream health were found again in strong numbers.

Fish Community

We recorded 47 species in 2025 and counted 7,891 individual fish across our surveys. Familiar species such as White Sucker, Central Stoneroller, Creek Chub, and several types of darters were seen at many sites. These species thrive when the water is moving, the streambed is stable, and the gravel is not covered with sediment. Their presence throughout the watershed suggests that many stream sections still offer these important features.

Top to bottom: Johnny Darter, Greenside Darter, Rainbow Darter, Fantail Darter

Darters in particular tell us a lot about the state of local streams. They live right on the bottom and rely on clear, well鈥憃xygenated riffles. The fact that we encountered several darter species in 2025 suggests that many riffles are still in good condition. These small fish are a favourite for kids as well, since their colours and quick movements make them fun to spot.

Biodiversity

Some areas stood out for the number of species they supported. Medway Creek had the highest species richness in 2025. The Plover Mills Corridor was close behind, while Cedar Creek, the Avon River, and the Middle Thames also showed strong diversity. These places tend to have a mix of shade, flowing water, cool pockets from groundwater, and patches of natural streambed. These features give fish more places to feed, spawn, and find refuge.

We also focused a fair amount of work in Cedar Creek, Medway Creek, the Middle Thames, River Bend, and the Plover Mills Corridor. Monitoring these areas year after year helps us understand long鈥憈erm trends and supports restoration and stewardship efforts with good information.

Want to know where these watercourses are? Check out the Watershed Report Card maps!

Sensitive Species

Northern Sunfish

Two Species at Risk appeared again in 2025. Each one helps us understand where healthy habitat still exists or has recovered.

Northern Sunfish were found mostly in Cedar Creek and the Avon River, with smaller numbers in Medway Creek and the Plover Mills Corridor. These fish like calm, plant鈥憆ich waters, so their presence suggests that these areas offer quieter, vegetated habitats. We counted 23 Northern Sunfish in total.

Black Redhorse were most common in the Plover Mills Corridor and Medway Creek, with one record in the Middle Thames. These fish need clean gravel and steady flows, so their continued presence is an encouraging sign that some riffles remain relatively free of silt. We recorded 16 Black Redhorse this season.

We did not record any Silver Shiner in 2025. We will continue to keep watch for this species in the coming years.

2025 Results and Watershed Health

Taken together, these results show that many sections of the Upper Thames River watershed still provide the conditions fish need to survive. Streams that had shaded banks or well鈥慹stablished vegetation tended to support more kinds of fish. Short stretches of good habitat, even when surrounded by more modified sections, work like stepping stones that help fish move through the system.

We recorded watercress at 32 of our sampling sites. This aquatic plant often grows where groundwater enters the stream, which creates cooler pockets of water during hot weather. These small, natural cool spots help fish manage warm summer conditions.

Even though there are always challenges such as summer heat or eroding banks, the overall story from 2025 is one of resilience. The fish communities we observed are holding together in many parts of the watershed, and the areas that are doing well help support the ones that are under more pressure.

Stewardship of the Thames

Good conditions in the water start with small, everyday choices along the land. Simple steps like keeping roots in the ground near creek edges, maintaining shrubs or trees where possible, and paying attention to areas of exposed soil help keep streams stable and clear. Clean gravel and shaded sections give fish places to thrive, and these features can exist in both rural and urban settings.

Students exploring the water with nets, families enjoying a neighbourhood trail, and landowners caring for a strip of vegetation all contribute to the health of our local streams. When these small efforts add up along the length of a creek, the whole river community benefits.