One of the world's biggest uranium miners is expecting to post half yearly losses of up to $US50 million as wet season rains continue to delay its operations.

Energy Resources of Australia says the tailings dam at the Ranger uranium mine inside Kakadu National Park is still close to capacity.

In January, ERA announced it was suspending operations at its processing plant inside the world-heritage listed area because the dam was nearly full.

It was expecting to start up the plant again this month but in an announcement to the stock exchange, the company says it's now further delayed the reopening of the plant until late July because of wet season rains.

ERA says uranium oxide production is down 42 per cent on the same time last year.

It's also expecting to post a net loss of between $US30 million and $US50 million for the first half of the year.