Seattle voters have an extra reason to turn out for this year’s Aug. 5 primary election: whether or not to create a city park district to help fund parks and recreation programs.

That ballot measure, known as Proposition 1, will be one of the questions facing city voters in ballots being mailed this week. Returned ballots must be postmarked by Aug. 5.

Around the region and state, Washington voters will choose their preferences in primaries for all 10 of the state’s U.S. House seats, as well as the entire state House and half the state Senate. Snohomish County voters will also vote in the primary for choices to fill the one-year unexpired term of former County Executive Aaron Reardon, who resigned last year.

The top two candidates in all races move on to the general election, regardless of party affiliation.

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David Ammons, communications director with the Secretary of State’s Office, said he predicts voter turnout will be average for a midterm primary, about 40 percent.

Voters must pay postage on ballots they mail in. No postage is needed for ballots put in drop boxes found at schools, libraries and other government buildings.

Four statewide elections for state Supreme Court will go straight to the November general election, according to Ammons.