Environmental groups are suing the Navy in an effort to halt plans for an offshore training range that they say would threaten endangered right whales.

The Southern Environmental Law Center says in the lawsuit filed Thursday that the Navy did not properly assess how the range would affect whales off the coasts of Georgia and Florida.

The Navy last year announced plans to begin laying underwater cables and sensors across 500 square nautical miles for training exercises involving ships, submarines and aircraft. The Navy has maintained it would have a negligible impact on the whales.

Conservation groups say the planned training area is too close to waters where right whales migrate each winter to give birth to their calves. Researchers estimate as few as 300 of the giant whales remain.