Residents who use King County rivers in unincorporated areas to swim or boat will soon be required to wear life vests.

King County Executive Dow Constantine signed Tuesday the life vest ordinance adopted Monday by the Metropolitan King County Council. Constantine proposed the ordinance to the Council earlier this month. The ordinance takes effect on July 1 and will remain effective through Oct. 31.

The measure calls for a public education campaign to alert residents of the new requirement by posting signs at primary access points to major rivers, and to promote life vest use in partnership with regional organizations focused on drowning prevention, such as Seattle Children’s Hospital and the Statewide Drowning Prevention Network.

The King County Sheriff’s Office will enforce the wearing of a U.S. Coast Guard-approved personal floatation device, or PFD, in the unincorporated portions of the Snoqualmie, Tolt, Cedar, Green, White, Raging and Skykomish rivers that run outside of cities.

First infractions for failure to wear a personal flotation device carry only a warning. Secondary infractions carry a fine of $86.

Health and safety officials will evaluate the program, along with feedback from emergency first responders and the public, to determine whether changes are appropriate and whether to propose that the requirement should become permanent.

“This  will help save lives,” said Constantine in a media release when he proposed the measure. “River flows are unusually swift and cold this year due to a heavy mountain snowpack that is melting into King County rivers. Rivers are inherently dangerous places to play, but this year is bringing additional risks. The wearing of life jackets is as essential for swimmers and boaters as helmets for cyclists and seat belts for drivers.”