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Upper Thames River Watershed moves to Level 2 Low Water Condition (low water update, October 24, 2025)

The summer’s below normal rainfall and above normal temperatures have continued into the fall, resulting 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 support healthy aquatic habitat.

The Ontario Low Water Program was developed to 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.

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:

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

The Province’s Low Water Response webpage has a .

UTRCA Watershed Conditions

30 Day Precipitation

The UTRCA measures precipitation at more than 20 locations across the watershed. The watershed received between 13 and 80 mm of rain from September 15 to October 15, 2025, with an average of 48 mm recorded (56% of normal). The long-term average for this period is 86 mm, measured at the London Airport and reported by Environment and Climate Change Canada (ECCC).

90 Day Precipitation

The watershed received between 101 and 214 mm of rain from September 15 to October 15, with an average of 146 mm recorded (59.6% of normal). The long-term average for this period is 246 mm, measured at the London Airport and reported by ECCC.

A Level 2 Low Water Condition is triggered if the three-month total precipitation falls below 60% of the long-term average.

18 Month Precipitation

The 18-month (April 2024 – September 2025) precipitation measured by ECCC at the London Airport totaled 1375 mm (96% of normal). The 18-month long term average precipitation total for September 30 is 1438 mm.

Monthly Streamflow

The UTRCA measures stream flows at more than 30 stations across the Thames River and many tributaries. The 30-day average stream flows for October 15 were at or below the long-term 10^th percentile flow rates for this time of year, indicating very dry conditions.

Smaller watercourses are affected more than the main North and South Thames Rivers, which are supported by water released from the UTRCA’s reservoirs at Wildwood (St. Marys) and Pittock (Woodstock) Conservation Areas, respectively. Water is stored in these two reservoirs during the spring runoff, and then slowly released in the dry summer and fall months to increase downstream flows in the main rivers.

Recommendation

Based on the 90-day precipitation totals across the watershed being below 60% of the long-term average (Level 2 trigger), combined with low percentile 30-day stream flow, it is recommended that the Upper Thames River watershed move to a Level 2 Low Water Condition.