NORFOLK, Va. (AP) — The U.S. Navy says about 10 percent of the whales it encounters near the Chesapeake Bay have shown signs of impact with ships.

That rate is pretty high compared to other areas, The Virginian-Pilot reports. Four juvenile humpback whales have recently washed up on Virginia’s shores, most likely killed by propellers.

The Navy is required to monitor whales along the Atlantic and Pacific coasts if its ships are going to train in the ocean.

Navy ships have lookouts and more maneuverability when it comes to avoiding whales. But the challenge is greater for larger civilian container ships. Pleasure boaters also pose a risk if they sail too close to the mammals.

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Information from: The Virginian-Pilot, http://pilotonline.com