Mattole Estuary and Lagoon
Estuaries provide an important transitional connection between freshwater and oceanic habitats in salmon life cycles. A critical habitat area, salmon utilize estuaries not only as a transitional migration zone, but also as nursing habitats.
The mouth of the Mattole is considered a bar built estuary and its characteristics change depending on the season. Sediment deposition from ocean currents and reduced river flows during the summer months causes the formation of a sand bar along the mouth of the Mattole. As a result, a lagoon forms behind the bay barrier. The depth and area flooded by the lagoon are determined by river flows and sediment deposition within the river channel. Scouring of the sandbar occurs during the fall with the onset of seasonal rain. Combined with erosion caused by waves, the estuary generally opens again in October.
Both natural processes and human land use have significantly impacted the Mattole estuarine environment. Sedimentation has contributed to filling estuary pools, reducing riparian canopy, and increased water temperatures. Historical accounts indicate the estuary had a narrower channel with coarser substrate, deeper pools, and denser tree populations on the floodplain. Changes in the Mattole estuary have affected salmon populations by reducing abundance of suitable juvenile rearing habitat.
