RCW 58.17.120: Disapproval due to flood, inundation or swamp conditions—Improvements—Approval conditions.

The city, town, or county legislative body shall consider the physical characteristics of a proposed subdivision site and may disapprove a proposed plat because of flood, inundation, or swamp conditions. Construction of protective improvements may be required as a condition of approval, and such improvements shall be noted on the final plat.

No plat shall be approved by any city, town, or county legislative authority covering any land situated in a flood control zone as provided in chapter 86.16 RCW without the prior written approval of the department of ecology of the state of Washington.