Declares that RCW 90.03.370 does not apply to impoundments of less than one hundred acre-feet provided that the facilities impound water under an existing water right where the use of the impoundment: (1) Facilitates efficient use of water and eliminates the diversion of water from the natural course of a stream or river during its base flow period;

(2) Promotes compliance with an approved recovery plan for endangered or threatened species or a watershed management plan that specifically provides an effective means to protect the water left in the stream during the base flow period; and

(3) Does not expand the number of acres irrigated or the annual consumptive quantity of water used.