Forget haunted houses — the spookiest show in Puget Sound this October is happening a few feet underwater, clinging to the underside of floating docks. Dubbed Docktober, the citizen-science tradition invites people to lean over dock edges and document the hydroids, nudibranchs and other creatures hiding in plain sight. Roughly 40 people turned out for one such meetup at a marina near Olympia, Washington, two weeks ago.
As reported by KUOW, Sidney Gerst organized the Olympia-area event. Roberts coined Docktober as a way to celebrate life on human-built marine infrastructure and has organized dock-fouling meetups around Puget Sound. Roberts describes the practice simply: exploring the organisms that colonize docks rather than natural shoreline. Participants document and upload their findings to iNaturalist, a citizen-science website, so researchers can make use of the observations.
Dock fouling itself is essentially tide pooling without the tide. As Oregon Public Broadcasting put it, “‘Dock fouling’ is like tide pooling, but at the docks,” inviting people to join citizen scientists already peeking beneath them. Because floating docks stay accessible through the fall and keep marine creatures submerged, they function as a sort of vertical tidepool that researchers at Nature Lookings describe as home to hydroids, bryozoans, tunicates, anemones, worms, crabs, sea stars, algae and nudibranchs.
Why October Brings the Best Viewing
October is an ideal time for dock fouling, according to Roberts, since nudibranchs are abundant on many Puget Sound docks this time of year. That timing matters because, per the same account relayed by KUOW, October low tides on Puget Sound occur late at night and aren't especially low — making floating docks a far more practical viewing spot than waiting on an exposed beach after midnight.
Puget Sound hosts more than 100 nudibranch species, ranging from creatures less than a millimeter long to footlong rainbow varieties, according to the Kitsap Sun. Roberts has reported seeing giant rainbow nudibranchs — among North America's largest species — consistently in the Olympia area for five years, and the orange-peel nudibranch is also found in Northwest waters. Some of the sea slugs have an unusual defense trick: the Kitsap Sun reports that nudibranchs have evolved to digest the stinging cells of the anemones they eat, so those stingers reappear on the nudibranch's own exterior. Elsewhere, a surge in Hopkins' Rose nudibranch populations off California's coast has served as an indicator of warming seas and climate change, per the same outlet.
Skeleton shrimp were another highlight at the Olympia-area meetup. Roberts said the creatures were abundant on the dock that day, and KUOW notes they can change color like chameleons and carry toxins in unusually large front claws. Hydroids — stationary animals related to sea anemones — rounded out the list of finds. Among the people drawn to the dock were Ghader Alrashid, who became interested in marine life after seeing her first sea star on the Oregon coast in 2025 and tide-pooling for the first time this year, and Warren Lee, who drove from Seattle to attend.
Ground Rules for Would-Be Dock Foulers
Roberts has laid out etiquette for anyone hoping to try dock fouling themselves: get permission from dock owners first, avoid obstructing boat users, and look at delicate marine animals without touching them. Roberts has also asked participants not to publicly share specific site locations, citing concerns about overcrowding, harm to the organisms, or dock owners revoking access.
What's Fouling the Hulls Above the Water
While dock-dwelling critters are the stars of Docktober, the same buildup process that creates habitat underwater is exactly what boat owners try to prevent on their hulls. Anti-fouling paint is used to keep boat hulls clean and improve their movement through water, and the coatings also help prevent boats from spreading invasive species, according to KUOW's reporting. But the most popular anti-fouling paints work by leaching copper into the water, which kills target organisms — and can kill salmon as well. Washington's Department of Ecology notes that copper is highly toxic to fish and other aquatic species, interfering with their sense of smell and reducing their ability to find their way back to spawning streams.
Washington state attempted to ban copper-based boat paints, with KUOW reporting the ban was postponed indefinitely after scheduled effective dates in both 2018 and 2026. State law, per the Washington Revised Code, makes the restriction on recreational-vessel antifouling paint containing more than 0.5% copper conditional on Ecology determining that safer and effective alternatives are feasible, reasonable and readily available. Ecology says the restriction will not take effect in 2026. Iris Deng, cited by KUOW, said a safer, effective alternative to copper has not yet been found — part of why Washington's Department of Ecology has reviewed potential biocidal and non-biocidal alternatives to copper-based paints under direction from the state Legislature.
Heavy fouling has had serious consequences before. In 2017, a Cooke Aquaculture net pen near Cypress Island in Skagit County failed, releasing approximately 250,000 non-native Atlantic salmon into Puget Sound, according to KING 5. The netting had become clogged with tons of mussels, anemones and algae, and photographs showed the fouling was so severe that the net itself was no longer visible, the Seattle Times reported at the time. Tidal currents eventually tore the structure apart. State investigators later said the excessive buildup of mussels and other marine organisms, caused by the company's failure to properly clean the nets, was the primary cause of the collapse, according to Washington's Department of Ecology. The disaster ultimately led the state's Board of Natural Resources to pass a ban on commercial net-pen fish farming on state-owned aquatic lands.
Back at the dock near Olympia, though, that same fouling that doomed a commercial operation is exactly what draws Docktober's citizen scientists back year after year — proof that one operation's maintenance failure is another explorer's miniature ecosystem.
