Olympic mudminnow
(Novumbra hubbsi)

The Olympic mudminnow (Novumbra hubbsi) is a fish native to the western lowlands of Washington: the Chehalis River basin, Deschutes River basin, and some Olympic Peninsula basins. It grows to 8 cm (about 3 in) in length, and it is the Washington only known endemic freshwater fish species. Although they strongly resemble killifish, mudminnows are more closely related to pikes.

The Olympic mudminnow is the only living species in the genus Novumbra, and one of eight living species worldwide in the paraphyletic family Umbridae. It predominantly resides in darkly stained tannic waters in the lower levels of lentic ecosystems, although may be found in clearwater swamps, and feeds on fish larvae, eggs, but more often small invertebrates. It prefers areas with mudbeds and dense vegetation, and has a remarkable tolerance for low oxygen levels.

The Olympic mudminnow is listed as a sensitive species by the state of Washington. Although many populations are found, the range is limited, and suitable habitat is easily lost to development.