BALTIMORE COUNTY, Md. (WJZ) — As summer nears and more people headed to beaches and pools to cool off, Baltimore County officials are reminding residents that swimming in the three city-owned reservoirs in the county is illegal.

Prettyboy, Loch Raven and Liberty reservoirs are dangerous for swimmers due to varying depths, hidden rocks, fallen trees and underwater currents, the county said.

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“No Swimming” signs are posted at all three reservoirs.

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It can also be deadly — each year, the county averages between five and 10 drownings and near-drownings, many in bodies of water where swimming is prohibited.

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Even in bodies of water where swimming is allowed, such as some rivers and streams running through state parks, officials urge caution and recommend only swimming in areas where a lifeguard is on duty.