SEATTLE (AP) — Boaters and vessel operators would not be able to release sewage, treated or untreated, into Puget Sound under a proposal by Washington state regulators.

The Department of Ecology says on its website that it petitioned the U.S. Environmental Protection Agency Thursday to designate the waters of Puget Sound a "no discharge zone" to improve water quality and protect shellfish beds and swimming beaches from harmful bacteria.

If approved, the zone would cover waters from near Sequim to south Puget Sound to the Canadian border, and includes Lake Washington and Lake Union.

There are dozens of no-discharge zones in the country, but this would be the first in the Pacific Northwest.

Critics say the proposal will be costly for many who would have to retrofit their vessels to accommodate sewage holding tanks. They say marine sanitation devices used on board by vessels treat sewage before it's dumped overboard.