Seattle geologist and author David B. Williams
The City of Seattle has at least fifty streams flowing across its ridges, through meadows and wetlands into bodies of water including Puget Sound and Lake Washington.
There is no one source for a list of Seattle streams and their names. Geologist and naturalist David B. Williams has compiled his research into the stream names, which is a journey into Seattle history.
Undated photo of John Thornton, courtesy of Clallam County Historical Society.
Like the names of Seattle streets, stream names can refer to historical figures such as Seattle’s early white settlers. Henry Yesler, who arrived in 1852, was one of Seattle’s earliest businessmen, owner of a sawmill which provided employment. A stream area named for him is in northeast Seattle, Yesler Swamp, adjacent to the Center for Urban Horticulture. In that neighborhood which is now Laurelhurst, Yesler later set up another sawmill on Union Bay.
One of northeast Seattle’s major stream systems, Thornton Creek, might have been named for John Thornton who arrived in Washington Territory in 1850 but who never lived in Seattle. The 1889 map of land claims is marked with the name Thornton Creek but does not clearly show who that name refers to.
Some tributaries of the Thornton Creek system are named for early residents such as the Fischer Farm family of Meadowbrook, the Willow Creek tributary at the Nishitanis’ Oriental Gardens nursery business, the Mock family who were neighborhood activists and John Matthews whose property became Matthews Beach.
Here is a link to David B. Williams’ list of stream names in Seattle. Check out his Walks and Talks page, as well, to find out when you can hear Mr. Williams at a book talk or go with him to explore the geology of Seattle. Mr. Williams’ newly republished book, Stories in Stone, tells of downtown Seattle buildings. Mr. Williams regularly leads walks to discover the types of stone used in downtown Seattle buildings, and he traces the downtown Seattle waterfront to talk about its changes over time.
Wedgwood in Seattle History 
Those names could be challenging and interesting for genealogists.
I wonder how many different names a stream has depending on how long it is and how many neighborhoods it crosses
Yes! That’s what happened in the Thornton Creek watershed. Early residents referred to the tributaries by the name of the nearest family, such as Becker’s, and Matthew’s for John Matthews of Matthews Creek. The name Thornton for the entire watershed, is of uncertain origin as I haven’t found why it is named that. I speculate that it could be an honorary name for John Thornton, an early settler in Washington Territory who served in the legislature, but he didn’t live in Seattle.