Be careful if you’re planning to float the Cedar River this summer, there’s going to be some obstacles near the lake.

After spending a week moving equipment into position and getting the river ready for its work, the city began dredging the lower Cedar River this week to remove 120,000 cubic yards of gravel in an attempt to prevent future flooding.

The project encompasses about a 1.25-mile stretch of the river from Lake Washington up to the Williams Avenue Bridge. Last week, the contractor, Gary Merlino Construction Co., moved dirt and rocks into the river in order to position the dredges and begin scraping the bottom.

The work must end by Aug. 31 in order to allow for salmon spawning this fall.

The Cedar is a man-made channel built in the early 20th century. The grade of the final stretch is relatively flat and collects deposits of gravel and debris that are washed down from higher ground.

After flooding in 1990, a review by the Army Corps of Engineers concluded that regular dredging, along with additional levees and flood walls that were built, was the best way to deal with the issue.

The last time the river was dredged was 1998.

The work this summer will be done with a trapezoidal dredge with an average depth of 4 feet. There will be a gradual slope from the North Boeing Bridge to Logan Avenue, with a steeper transition from Logan to Williams Avenue.

Once completed, additional mitigation efforts, including bank stabilization and habitat replacement, will take place.

The Cedar River Trail remains open and is expected to stay that way through the summer, with some occasional closures and detours when the work necessitates.

The approximately $7.5 million project is being funded by a grant from the King County Flood Control District.