The ocean is the ultimate destination of water flowing through coastal streams, but in some cases it may make an extended pit stop in a seasonal lagoon. A lack of rain and low flows during summer months combined with ocean wave action can build up a sandbar at the mouth of a river, thereby forming what is known as a bar-built estuary. This seasonal barrier means migratory fish like steelhead (Oncorhynchus mykiss) living in such streams have to wait for winter storms to carve them a path to the ocean. Far from being a prison, the lagoon provides valuable rearing habitat for young steelhead as they prepare to head out into the big blue.
However, many questions remain about how these fish make use of the productive habitat without suffering from the harsh environmental conditions that are characteristic of lagoons. In an effort to get some answers, scientists from the National Marine Fisheries Service in Santa Cruz monitored water quality and steelhead movement in a small coastal estuary in northern California across a season of lagoon closure (Bond et al. 2021). Their findings recently published in the journal Estuaries and Coasts suggest that young steelhead moved throughout the system strategically to maximize their growth while limiting their exposure to the challenges of fluctuating temperature and salinity.