Hosted by Seattle Iranians, this is a public “picnicing together,” event, free and open to everyone, at Lake Sammamish State Park in Issaquah Washington.

What is Sizdeh Bedar?
The thirteenth day of the New Year festival is called Sizdah Bedar (meaning “thirteen outdoors”). It often falls on or very close to April Fool’s Day, as it is celebrated in some countries. People go out in the nature in groups and spend all day outdoors in the nature in form of family picnics. It is a day of festivity in the nature, where children play and music and dancing is abundant. On this day, people throw their sabzeh away in the nature as a symbolic act of making the nature greener, and to dispose of the bad luck that the sprouts are said to have been collecting from the household.

The thirteenth day celebrations, Seezdah Bedar, stem from the belief of the ancient Persians that the twelve constellations in the Zodiac controlled the months of the year, and each ruled the earth for a thousand years. At the end of which, the sky and the earth collapsed in chaos.
Source: WelcometoIran.com

A Discover Pass is required at Lake Sammamish State Park.