https://openstreetmap.org/copyright | https://openstreetmap.org |
Copyright OpenStreetMap and contributors, under an open license |
https://openstreetmap.org/copyright | https://openstreetmap.org |
Copyright OpenStreetMap and contributors, under an open license |
I think I remember seeing that it is something like landuse=basin + basin=detention maintained by Seattle Public Utilities for stormwater management. Will try to dig up a source.
Supporting evidence in the meantime... there's a big ol' drain pipe outlet visible from aerial on the west side.