[1] From its headwaters on the Rose Hill moraine to its outlet at Juanita Bay is c. 2 miles (3.2 km) as the crow flies.

The southern extent is irregular trending roughly from Kirkland's high point at the northeast corner of Bridle Trails State Park (535 ft (163 m), 47°39′26″N 122°10′21″W / 47.65722°N 122.17250°W / 47.65722; -122.17250[2]) through South Rose Hill Park, to Lake Washington at 16 feet (4.9 m) above sea level.

The two join north of the lake then run west through a two-meter culvert under Interstate 405 near NE 100th Street,[4] under the Cross Kirkland Corridor, into the Forbes Creek Valley and Juanita Bay Wetlands Park.

The Forbes Creek watershed is a 1,837-acre (743 ha) drainage basin covering a quarter of Kirkland's total land area.

The landforms and hydrology of the Eastside, including Forbes Creek, are due to the ice age glaciation.

[22] The park also is home to many mammal species including beaver, muskrat, nutria, raccoon, river otter, weasel, and coyote.

[23] The Forbes Creek wetlands are noted as prime urban birdwatching areas by The National Geographic Society, Reader's Digest, and many Pacific Northwest guidebooks.