RCW 35.56.200: Waterways constructed—Requirements.

In the filling of any marshland, swampland, tideland or tideflats no canal or waterway shall be constructed in connection therewith less than three hundred feet wide at the top between the shore lines and with sufficient slope to the sides or banks thereof to as nearly as practicable render bulkheadings or other protection against caving or falling in of said sides or banks unnecessary and of sufficient depth to meet all ordinary requirements of navigation and commerce.