There's no single GPA requirement to play high school sports in Washington state. Eligibility rules are set by each individual school district, and sometimes even by individual high schools within those districts. While a minimum GPA might not be explicitly stated, most districts will have academic eligibility requirements, often involving maintaining a passing grade in all classes or a minimum grade point average (often around a 2.0, but this varies).
To find out the specific requirements, you need to check with your high school's athletic director or the school's website. They'll have the most up-to-date and accurate information on eligibility.