How do you tell if a lake is contaminated?

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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Look for signs of poor water quality, such as algal blooms and dirty or turbid water. Do not swim in water that smells like rotten eggs or sewage. Avoid swimming near pipes that drain into lakes or streams.

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A boil water advisory is issued when harmful germs (e.g., E. coli bacteria, Giardia parasite) may be in a drinking water supply. Drinking water contaminated with these germs can make people and animals very sick. Boiling will kill the germs and make the water safe to drink.

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If there is scum or algae visible in the water, it won't be clean enough to swim in. There are also natural hazards to outdoor waters compared with pools, especially in the summer. Blue-green algae is a type of bacteria naturally found in lake ecosystems.

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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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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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