The federal government has moved to dismiss a lawsuit brought by New Jersey environmental officials against a research project that blasts the ocean floor with sound waves, mainly because the project is already finished.

The U.S. Justice Department has asked a federal judge to dismiss the suit brought by the New Jersey Department of Environmental Protection against several defendants, including the National Science Foundation.

The project used sound waves to study sediment on the ocean floor dating back 60 million years, to see how sea level rise has changed the coastline.

But environmentalists say it could harm marine life.

The government says the work is already over and there are no plans for additional similar tests.

Opponents say important procedural issues were not dealt with before the test started.