The Grey Sauble watershed is under a flood watch following about 25 mm of rain in just six hours overnight.
That's on top of the between 75 and 120 millimetres the region received over the past three days.
Heavy rainfall is already causing flooding problems in parts of the Grey Sauble watershed.
Officials say areas of South Bruce Peninsula and Georgian Bluffs are reporting road closures due to high water.
Unusually elevated levels have also been recorded in Gould Lake, Hepworth Creek and Spring Creek in Hepworth, as well as Parkhead Creek in Shallow Lake.
Flooding is being reported in low-lying areas, and there is concern that additional rainfall forecast for the next two days could lead to more road closures and limited access to some areas
Levels in most large water systems in the watershed should peak later Wednesday and exceed normal spring levels, but will not reach the high levels seen earlier this spring. However, parts of the Sauble River and Sydenham River system are expected to continue to rise overnight and into Thursday, possibly reaching or exceeding levels already seen this spring.
Gould Lake, Hepworth Creek/Spring Creek in Hepworth, and Parkhead Creek through Shallow Lake are seeing unusually high water levels.
More rain is on the way. A special weather statement from Environment Canada forecasts another 20 mm of rainfall by Thursday in the northern sections of midwestern Ontario.
Huron and Perth Counties could see between 20 and 50 mm more rain in the next day.
The Ausable Bayfield and Maitland Valley Conservation Authorities have issued a flood outlook message. Both the ABCA and the MVCA expect rising water levels to peak at or near bank-full conditions, but higher rainfall amounts could lead to water spilling over, causing minor, localized flooding within traditional flood plain areas
Local Conservation Authorities are warning that fast-moving water and unstable banks near rivers and streams create dangerous conditions.
Residents are being urged to stay away from waterways and monitor local conditions closely.
Conservation authority staff are expected to continue tracking water levels and weather conditions and will provide updates as needed.
