The 9-Foot Pipe Under SR 527 That Decides Where Penny Creek's Salmon Can Go

Just south of the 164th Street SE intersection, Penny Creek passes under SR 527 through a culvert 9 feet wide and 4 feet tall. Upstream are more than 8 miles of creek that fish can't reach. WSDOT plans to replace the culvert with a 26-foot span, and the work will close the highway for at least two full weekends. WSDOT's public project page has said for a while that construction starts in spring 2027. WSDOT's own contract schedule, updated in September, now points to a later date.

Both the fish and the closures depend on that one structure, so it helps to know what the pipe does now, who uses the creek on either side of it, and why the timeline on the project page has fallen behind.

A creek that runs through backyards before it reaches the highway

Penny Creek is a Mill Creek creek from start to finish. The SnoKing Watershed Council traces it from the Penny Creek Natural Area through the Mill Creek Country Club golf course, then through the Mill Creek Community Association Nature Reserve. From there it passes under SR 527 just south of Mill Creek Road and joins North Creek. The council's stream report includes a photo caption that will make golfers smile: golf balls from the course often end up in the creek.

Fish trouble on this creek goes back a long way. A resident's history of the area in the MCCA's MillStream newsletter describes an old farm pond and a fish ladder built so migrating fish could get past a dam. The ladder was repaired in 1998. The writer quotes Tom Murdock of the Adopt-a-Stream Foundation, who said Penny Creek historically had coho salmon, steelhead, and cutthroat trout. The writer also notes that before Mill Creek was developed, coho migrated through every winter. According to the same account, fish are still in the creek but hard to see, and the large ones move mostly at night during winter high water.

That last detail matters for anyone hoping to spot one. Penny Creek isn't a viewing creek with a parking lot and a sign. It's a working stream, and most of what happens in it happens out of sight.

Three ways a culvert stops a fish

WSDOT lists three separate problems at the SR 527 crossing. Erosion has left a drop-off at the culvert, so the opening sits too high for fish to jump into. The pipe is so narrow that water moves faster than fish can swim against it. Old log weirs were added to the stream to manage flow, and they are now too tall for fish to clear.

Any one of those would be a barrier. Together, they explain why WSDOT is replacing the structure instead of patching it. The new structure will be 26 feet wide and 10 feet tall. WSDOT also plans to add woody vegetation, logs, and other wood to create pools where young fish can take refuge. WSDOT's design standard requires that the stream work for fish of every age in every season. That means usable water for juveniles in the low summer flows and resting spots for adults in the fast winter water.

Here is what the replacement opens up, by WSDOT's count:

• 8.36 miles of habitat that fish can't reach now
• 9.71 acres of rearing habitat, where young fish live and grow
• 0.86 acres of spawning habitat for adults

The estimated cost is $8 million, all state money. The project is part of WSDOT's statewide fish passage program, which builds fish-passable structures under highways across western Washington. The program exists because a federal court injunction, made permanent in March 2013, requires the state to fix road culverts that block salmon migration.

October is already on Penny Creek's salmon calendar

WSDOT's species calendar for Penny Creek shows why the timing matters to the fish too.

By WSDOT's calendar, four of the five are listed for October, and steelhead start next month. WSDOT doesn't break out how many reach the SR 527 crossing, but the culvert is the barrier it says keeps fish out of the 8.36 miles above it. North Creek is easier to watch. A ParentMap listing for North Creek Trail Park in Bothell suggests looking for sockeye in October and coho in November, checking under bridges, and bringing polarized glasses for glare. Penny Creek's own fish, as the MillStream account points out, mostly keep to the dark and the high water.

The two weekends, and why they are probably not next spring

For drivers, the impact is specific. WSDOT says SR 527 just south of 164th Street SE/Mill Creek Road/Seattle Hill Road will likely drop to one lane in each direction overnight during the project. Building the new structure will also take at least two weekend-long full closures. WSDOT has already mapped the detours:

1. Northbound: SR 524, North Road, and 164th Street SE.
2. Southbound: Mill Creek Road/Seattle Hill Road, 35th Avenue SE, and 180th Street SE.

WSDOT estimates each detour adds about three miles to a trip.

The question is when. The project page gives a timeline of "2024 - Early 2027" and lists the project as pre-construction. Further down, the same page lists design through 2026, contractor advertising in late 2026, construction in spring 2027, and completion in fall 2027. Even on its own page, the headline timeline and the milestones don't agree.

WSDOT's Advance Schedule of Contracts, updated September 14, 2026, gives a different date. It lists contract A52714B, "SR 527/Penny Creek - Fish Passage," for advertisement on August 16, 2027, in a $5 to $10 million range. A contract has to be advertised before it can be bid, awarded, and built. An August 2027 ad date would put construction after the spring 2027 start shown on the project page.

WSDOT notes that advance-schedule dates are tentative and depend on funding, so August 2027 isn't fixed either. As of early October 2026, no contract for this project had been advertised, bid, or awarded. The most recent WSDOT bid opening found, dated September 23, 2026, was for an unrelated project. WSDOT says it will announce the exact dates of the overnight lane reductions and weekend closures closer to construction. The project page links to WSDOT's email updates, and Eric Zackula of WSDOT Communications is listed as the project contact.

Mill Creek has other fish pipes on the books

The SR 527 crossing is the largest of several fish-passage projects on Mill Creek's creeks, and one of them belongs to the City. The City's capital project list includes "Nickle Creek/Old Seattle Hill Rd Fish Passage" (project SW00002), with $400,000 budgeted for 2026 and $1,575,000 for 2027, a total of $1,975,000. The adopted 2025-2026 budget moved its construction to 2027 and removed the expected grant revenue to match. A City capital plan adopted in 2004 described a Nickel Creek culvert replacement on Old Seattle Hill Road near the Lively Environmental Center that would also widen the road for a sidewalk and safety railing. That plan is two decades old, so the final design may differ. A separate Old Seattle Hill Road reconstruction (ST00007) is budgeted at $2.4 million across 2026 and 2027.

Upstream on Penny Creek's own system, WSDOT has a bigger project under I-5 near 112th Street SE in Everett. It covers three barriers, one of them on an unnamed Penny Creek tributary, runs Summer 2025 to Winter 2030, and is budgeted at $61.6 million. Closer to home, there is a culvert at the entrance to the Penny Creek Natural Area. The Herald reported in September that it sits in City right-of-way and would cost about $1 million to replace, separate from the state project.

What a wider pipe can't fix

Opening 8.36 miles of creek only helps if the water upstream can support fish. The SnoKing Watershed Council's volunteer monitoring on Penny Creek found that stream temperatures are usually safe for fish, but dissolved oxygen has dropped below healthy levels for salmon during several monitoring events. The report names construction activity and land use, including the golf course, as factors in water quality. Bacteria counts sometimes rise after heavy rain.

Homeowners have more say here than WSDOT does. The MillStream account says that if neighbors want fish in Penny Creek, they should keep chemicals and fertilizer off yards that drain into the stream and plant native plants along the banks for shade. It points readers to the Adopt-a-Stream Foundation for more. The state will replace the pipe on whatever schedule the contract allows. The water that runs through it afterward depends on the yards and lawns along the creek before it gets there.

If you live along Penny Creek or drive SR 527 every day and want to know how a project like this could affect your property or your plans, Jessica Gustelius is happy to go through it with you, from creek-side yards to closure weekends. Let's Connect.

This article is general information, not legal, tax or financial advice. Consult a qualified professional about your situation.