Why did they scrape the cement down there?
The Chittenden Locks are the passage between the fresh water lakes and Puget Sound not only for boats but also for the thousands of salmon migrating through the Lake Washington Ship Canal. While most of the fish use the fish ladder or smolt flumes, a small percentage do migrate through the locks (there's always some who don't follow the crowd!).
When the locks are filling or draining the water flow through the openings is fast and furious. Salmon can get brushed up against the sides of the lock chamber or pulled into the tunnels by the force of the water flow. Barnacles are scraped off to help eliminate injury to the fish. When the surfaces around lateral tunnels and the surfaces of the filling tunnels are smooth, the salmon are protected from being 'de-scaled' against the sharp edges of the barnacles.
The large lock is scheduled for refilling on Wednesday 11/25, the small lock is scheduled for it's annual draining/cleaning in March.
- Chittenden Lock Video (Seattle Times)
An amazing amount of sea life resides just inside the downstream gate of the large lock, these are 3 starfish waiting for re-filling.