State Route 53 (SR 53), also known as the Clearlake Expressway, connects SR 29 and SR 20 via the city of Clearlake. It runs in a north–south direction east of Clear Lake. The entire length of the highway is a California Scenic Highway.

SR 53 is part of the California Freeway and Expressway System and is eligible for the State Scenic Highway System. However, it is not a scenic highway as designated by Caltrans.

SR 53 begins at California State Route 29 in the town of Lower Lake, near Anderson Marsh State Historic Park. The highway then heads northward along Clear Lake, the largest freshwater lake located entirely in California. It bypasses the center of Clearlake, California, instead going through the neighborhood of Highlands Harbor, and ends at California State Route 20 north of the city limits.

Except where prefixed with a letter, postmiles were measured on the road as it was in 1964, and do not necessarily reflect current mileage. The entire route is in Lake County.