Isabel Creek is a 18-mile-long (29 km)[2][3] perennial stream which flows northwesterly along the eastern then northern flank of Mount Hamilton in Santa Clara County.

Hamilton when they climbed it on August 26, 1861, although they did place Isabel Valley on their map to the east of the mountain.

Steelhead trout (Oncorhynchus mykiss) are native to Isabel Creek, as noted by John Otterbein Snyder who collected specimens in 1898.

[9] Impassable falls are present on upper Arroyo Hondo, but the rainbow trout in Smith and Isabel creeks are assumed to be native, as California roach (Hesperoleucus symmetricus) and Sacramento sucker (Catostomus occidentalis occidentalis) are also present above and below the falls.

Speckled dace (Rhinichthys osculus) were collected by John Otterbein Snyder in 1898 in Arroyo Hondo and Isabel creeks, but not by Scoppettone and Smith in 1978, nor by Leidy and Bronwen in 2013, and their status in the creek remains uncertain as is true of most of their former sites in the central coast.