Are lakes safe after rain?

We call it the 48-hour rule, and it goes like this: In order to protect your health against recreational water illnesses, avoid contact with the water for at least 48-hours after a significant rain event. Think that sounds harsh? Some places suggest waiting up to 72 hours.



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Stay out of the water if Cloudy water can be a warning that there are more germs in the water than normal. Discolored or smelly water could mean there is a harmful algal bloom (HAB) in the water.

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Fast-moving currents, waves and rapids, even in shallow water. Hazards, such as dams, underwater obstacles, or rocks and debris. Vegetation, animals and fish. Drop-offs that can unexpectedly change water depth.

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Know before you go Before you head out, check online to find out if the swim area is currently monitored, is under advisory, or has been closed for health or safety reasons. This is especially important after a heavy rain.

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Lakes can be affected by pollution from various sources such as agricultural runoff, urban development, and recreational activities. High levels of bacteria, harmful algae blooms, and pollutants in the water can pose health risks to swimmers.

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During rainy seasons, oxygen concentrations tend to rise in most surface waters because rain saturates with oxygen as it falls. More sunlight and warmer temperatures also increase plant growth and animal activity, which may increase or decrease DO concentrations and increase diurnal fluctuation.

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Smelly or Discolored Water The smell or appearance of water can also indicate water pollution. Water contaminated with sulfur or certain bacteria will emit the smell of rotten eggs. High iron levels give water an orange color. High manganese levels will cause water to look purple or black.

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“No swimming” signs: This one should go without saying. If there are “no swimming” signs posted near the waterway, don't enter it! Chances are, there are concealed hazards underwater that you may not notice from up above. If you see a sign posted, don't risk it—it's better to find somewhere more desirable to swim.

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