- The park covers one acre with approximately 1,000 feet of saltwater shoreline on Spieden Channel. A maximum of 16 persons are allowed to camp overnight at the primitive water trail campsites on the island. There is one composting toilet. No drinking water is available on the island and garbage must be packed out.
Of special interest are the wildflowers that bloom from April through June.
This park is part of the marine parks and boat moorage system. Facility use is first come, first served, with continuous moorage limited to three consecutive nights. Fees are charged year around. Call (360) 753-5771 for a fee update as all fees are subject to change.
Recreation - Camping and wildflower viewing are popular island activities.
Climate - Washington's climate varies with each region. Posey Island State Park is located in an area "protected" by surrounding ocean waters and mountain ranges. Temperatures are consistently moderate, rarely topping 80 degrees in the summer and rarely falling below 30 degrees in the winter.
Annual rainfall averages 29 inches, approximately half that of Seattle. In the summer months, and especially during September and early October, the islands may go for weeks without a cloud in the sky. Snowfalls occur once or twice a year and usually total only one or two inches. Northeast winds may cause temperature extremes.
Island tides range over 14 feet. The extreme low tide of 4.0 feet to the extreme high tide of over 10 feet.
Posey Island State Park is located one-fourth mile from the northwest end of San Juan Island in San Juan County. It is accessible only by boat.