Watershed
The Napa River watershed encompasses approximately 426 square miles (1,103 km²). Larger tributaries, such as Dry, Conn, and Soda creeks, show signs of recent incision and have graded to the incised current level of the mainstem Napa River. In some cases, smaller tributaries cutting across the valley floor have not fully adjusted to the lowered level of the mainstem and are elevated at their confluence with the mainstem, forming potential barriers to upstream fish migration. Several large dams were built between 1924 and 1959 on major eastside tributaries (Conn, Rector, Milliken, and Bell dams) and the northern headwaters of the Napa River (Kimball Dam). In addition, many smaller dams can be found throughout the watershed. These numerous dams are impassable barriers to salmon and steelhead seeking their historic spawning grounds.
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