Closed now, open again the Saturday before Memorial Day
If you are reading this in late September, the Cedar is shut. The 2026-27 Washington rules open the river from its mouth to the Landsburg Road Bridge, at river mile 21.5, only from the Saturday before Memorial Day through August 31. Selective gear rules apply the whole time, which means artificial flies or lures with barbless single-point hooks, no bait, and knotless nets. There is a night closure and internal combustion motors are prohibited. Trout follow statewide size and limit rules except that cutthroat and wild rainbows must be released, and since Emerald Water Anglers in Seattle describes the Cedar's trout as native, treat every fish as a release.
Above the Landsburg Road Bridge to the falls, the river is closed water all year.
Why the fish got big
Emerald Water Anglers, which guides here, tells the history this way: the Cedar was closed to all fishing for years to protect its steelhead and salmon spawning runs, reopened in 2004 for three summer months, and local anglers have since fought to keep it catch-and-release with single barbless hooks. Because it was closed so long, the shop says, some of its trout have grown past 24 inches, and some anglers believe part of the rainbow population is of steelhead descent. The shop is just as clear about expectations: treat it as trophy water where a few good fish is a good day, not a fish every few minutes, and bring a rod that can handle them.
The other reason the river is in such shape is ownership. Upstream of Landsburg, the Cedar runs through Seattle's protected water supply watershed, and at Landsburg a dam diverts water into a 29-mile pipeline to the city. The watershed above it is closed to the public, and so is the river.
Twenty-one miles on foot
Emerald Water Anglers counts about 21 miles of fishable water between the mouth in Renton and Landsburg. The river runs west and north out of the watershed past Maple Valley and into Renton, where it passes under the Renton Public Library and empties into the south end of Lake Washington. It is close enough to fish after work and gets fished hard near the easy access points.
The shop's advice is to walk. Summer flows are low enough that the Cedar can be waded almost its whole length, fishing as you go, and the bigger trout are away from the parking spots. Its gear list is simple: a 3 to 5 weight with a floating line, and a fly box of Stimulators, Humpies, Adams, Royal Wulffs, Royal Coachmen, H and L Variants, grasshoppers, Copper Johns, Pat's Stones and Lightning Bugs, plus caddis.
Sockeye, and the fish you are not allowed to target
The Cedar is also Lake Washington's main salmon river. Chinook, coho, sockeye and steelhead use it, reaching it through the Ballard Locks, the Ship Canal and the lake rather than their old route up the Duwamish and Black rivers. Sockeye are the run in trouble: by the early 2020s only about 10,000 were counted making it past Lake Washington, and the Muckleshoot Tribe began trucking 1,500 spawners from the Ballard Locks to the Cedar.
The trout season closes on August 31 and the river stays closed through the fall. Salmon fishing in this system happens in the lake. As of September 18, 2026, WDFW had reopened coho retention in Lake Washington north of the 520 bridge and east of the Montlake Bridge through October 31, after Ballard Locks counts improved. The Cedar itself stays closed.
30 to 250 cfs, read at Renton
Emerald Water Anglers gives an ideal range of 30 to 250 cfs for the Cedar. This page applies it to the Renton gauge, USGS 12119000, near the mouth. Monthly means since 2010 there are about 590 cfs in June, 270 in July and 160 in August, so the river usually drops into the range as summer goes on, and June can still be too high to wade comfortably. The Landsburg gauge, 12117500, reads the top of the open water and runs higher than Renton in summer, around 390 cfs in July and 290 in August. On September 24, 2026, Renton read 271 cfs and Landsburg 341. For planning, the shop puts the river about 30 minutes from Seattle and runs half-day walk-and-wade trips of four to five hours of fishing, which is about the right length for a summer evening on the lower river.