Some of the best marine ecosystems to explore from a public access state park are located on Whidbey Island, the easiest and largest of the islands exposed to direct tidal flows that surge from the Pacific Ocean up into the Inside Passage. This rates as one of the top convenient dive sites in the Puget Sound.
Keystone is a favorite for those located along the upper I-5 corridor, as it is one of the most reasonable and convenient kelpy rock reefs you can get to as a day trip from the cities. The consistent currents here make it a bit more interesting than the standard beach parks like Alki, Edmonds, or Mukilteo.
The Washington State Ferries system was kind enough to install a sizeable jetty of giant boulders at Keystone to shelter the ferry terminal there from the strong weather and currents of the Admiralty Inlet, which acts as a giant reef habitat and tidal sieve for any and all marine species that swim, drift, crawl or slither. It is a major hangout that also attracts seabirds, pinnipeds, and divers, of course.
Currents can be challenging, deceiving, and perilous here, so it is recommended that you dive with someone who has experience with the site, a local dive shop, or guide. Staying calm, well-oriented, and near to the rocks is important, as is avoiding direct contact with the marine life that covers everything. Don’t swim ‘with’ a current unless you know from experience where it is going. Fighting a strong current here may be a losing battle that sucks you into the path of the ferry, or far and deep out into open waters! But this is very rare, thanks to mindful divers.
The jetty is a marine park and closed to fishing, spearing, taking, trapping or collecting–except on the part of the rocks that faces the ferry. Families take their kids fishing on the ferry side, and divers regularly explore and monitor the protected side. (Nearby Driftwood Park is better for salmon fishing, or a low-cost skiff to get out into the better fishing zones.)
The ‘Puget Sound’ refers to the network of enclosed waterways that connects the watersheds of the Greater Olympia-Tacoma-Seattle-Everett metropolitan corridor to the Pacific Ocean via the Strait of Juan de Fuca, and to the rest of the Salish Sea up into British Columbia via Rosario Strait. That’s a variety of names given by explorers and settlers of the near-modern era, and surely everything had additional names before that (like this, an impressive example).