Closure of the Port of Baltimore — America’s second-biggest hub for coal — has choked exports of the fossil fuel, with flows expected to plunge 35% this month.

Exports will slump 6.3% for the year, according to US Energy Department figures released Tuesday. A month ago, the agency was predicting shipments of the dirtiest fossil fuel would be 100.8 million tons but now expects 94.5 million tons.

Exports have been increasing in recent years as domestic utilities shift to cleaner fuels, making international markets increasingly important for US miners. Baltimore accounted for about 28% of US exports last year.

“We expect US coal exports to recover toward the end of the summer or early fall, but there is significant uncertainty based on the timeline for the port reopening,” Energy Information Administrator Joe DeCarolis said in a statement.

The harbor remains closed after a massive cargo ship crashed into a critical bridge last month, blocking ship traffic. The port could reopen for normal operations by the end of May after a limited-access channel is cleared.