King County has purchased two properties north of KVI Beach as part of its ongoing effort to protect a long stretch of naturally eroding bluffs and an imperiled salt marsh located at the beach, the best and largest one in the region.

The purchases, one completed Friday and another that closed in April, add 4.3 acres to the Point Heyer Natural Area, bringing the preserve to a total of 33.5 acres, with 1,500 feet of marine shoreline, according to Greg Rabourn, the Vashon-Maury Island basin steward at the county’s Department of Natural Resources and Parks.

The two parcels, both raw land, cost a total of $307,000. The money for the purchase came from the county’s Conservation Futures Fund, a pool of money that can be used only to protect conservation land and open space, Rabourn said.

Point Heyer, the place name for KVI Beach, contains the largest natural-barrier lagoon remaining in the county, Rabourn said. The county established the natural area a few years ago in an attempt to protect the lagoon and Point Heyer. By conserving the bluffs and shoreline north of the lagoon, the county is helping to safeguard a long stretch of naturally occurring erosion and tidal action, called a drift cell, that feeds Point Heyer, he said.

“When bulkheads are installed, it stops this process and depletes beaches,” Rabourn added. “We’d lose the salt marsh over time.”

The long stretch of shoreline and the marsh at KVI Beach are also important to Puget Sound’s salmon, and the protection effort at Point Heyer is part of the region’s long-standing effort to recover imperiled salmon runs, Rabourn said.

“It’s critical,” he said. “It’s a very high priority acquisition as part of the overall … salmon recovery effort in central Puget Sound.”