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Upper Thames River Watershed in Level 1 Low Water Condition (low water update, August 27, 2025)

This summer’s low rainfall and prolonged hot temperatures have resulted in low stream flows across the ÌÇÐÄÖ±²¥ (UTRCA) watershed. These conditions can have an impact on the amount of water available for human use, as well as the amount of water available to ensure a healthy aquatic habitat.Ìý

UTRCA Watershed Conditions

30 Day Precipitation

The Upper Thames River watershed received between 33 and 92 mm of rain between July 22 and August 21, with an average of 62 mm recorded (78% of normal). The long-term average for this period is 80 mm, measured at the London Airport and reported by Environment and Climate Change Canada (ECCC).Ìý

90 Day PrecipitationÌý

The Upper Thames River watershed received between 142 and 238 mm of rain between May 23 and August 21, with an average of 178 mm recorded (73% of normal). The long-term average for this period is 242 mm, measured at the London Airport and reported by ECCC.Ìý

A Level 1 Low Water Condition is triggered if the three-month total precipitation falls below 80% of the long-term average value.Ìý

18 Month Precipitation

The 18-month (February 2024 – July 2025) precipitation measured by ECCC at the London Airport totaled 1406 mm, or about 100% of normal. The 18-month long term average precipitation total for July 31 is 1410 mm.Ìý

Monthly Streamflow

The August 21, 30-day average stream flows were generally above the 25th percentile flow rates for this time of year, with the exception of Medway Creek and Fish Creek, which are both below the 20th percentile.Ìý

The UTRCA maintains three large reservoirs and several smaller ones across the watershed. Pittock Reservoir (South Thames River in Woodstock) and Wildwood Reservoir (Trout Creek above St. Marys) provide flow augmentation in the summer, meaning they store spring runoff and then slowly release this water back into the river system in the dry summer months. Both these reservoirs are currently adding to downstream flow.Ìý

Recommendation

Based on the 90-day precipitation totals across the watershed being below 80% of the long-term average (Level 1 trigger), but with still relatively normal 30-day stream flow, the Upper Thames River Low Water Response Team recommends that the Upper Thames River watershed move to a Level 1 Low Water Condition.

About the Low Water Program

The Ontario Low Water Program was developed to assist in coordination and support local response in the event of drought. Under this program, each Conservation Authority has formed a Water Response Team to provide information and recommendations to help local interest-holders and watershed communities reduce and better manage water use.Ìý

Precipitation and stream flows are the key low water indicators. The program provides the following definitions for the three-tiered system used to inform the public of local low water conditions:Ìý

• Low Water Level 1: Early indication of a potential drought condition.Ìý
• Low Water Level 2: Increased likelihood of drought conditions.Ìý
• Low Water Level 3: High likelihood of drought conditions (does not imply an emergency).Ìý

The Province’s Low Water Response webpage has a .Ìý