The Essex Region Conservation Authority said not enough rain has fallen yet for a flood watch, but it is concerned about standing water in low-lying areas.
It issued a watershed condition statement, which will remain in effect until 3 p.m. on Tuesday.
Rain gauges across the county recorded between 15 and 20 mm of rain within two hours on Monday night.
Low-lying areas in floodplains and near all major waterways and shoreline areas are of particular concern.
"The combination of slippery banks and fast-moving water can be dangerous," said the statement. "Standing water can also present its unseen hazards. Children, pets, and livestock should be kept away from flowing or standing water."
Environment Canada issued a special weather statement calling for heavy rainfall at times, with possibly an accumulation of up to 50 mm.
The authority will continue to monitor forecasts and said it would modify its advisory as required.
