Ocean scientists from NOAA are closely watching a variety of indicators to track the arrival of El Niño on the West Coast. While the waters off Southern and Central California are currently unusually warm, this warming is linked to a recent marine heat wave, not yet directly tied to the current El Niño. Most of the Pacific Coast is still experiencing relatively normal ocean conditions, but a strong El Niño could bring significant changes to the region in the coming months. In June, NOAA's National Weather Service officially declared that El Niño had developed, based on rising ocean temperatures in the tropical Pacific near the equator. However, the effects of El Niño on the West Coast usually take a few months to reach the region. Scientists from NOAA Fisheries are now monitoring shifts in ocean conditions and marine life to detect when El Niño's influence begins to be felt along the coast. One key indicator is changes in coastal sea levels, which are influenced by Kelvin waves—ocean currents that originate along the equator and travel northward. These waves reached California in May and June, but their impact on the West Coast is expected to be mild compared to what may happen later this fall and winter. As these waves move north, they can also affect water temperatures by deepening the thermocline, the layer in the ocean where temperature changes rapidly with depth. This can weaken the usual upwelling of cold, nutrient-rich water along the coast, leading to warmer nearshore waters from Baja California to Alaska. Biological changes are also being closely observed. Some fish species that prefer warmer water have already moved north along the West Coast due to previous marine heat waves. However, these movements are not reliable indicators of El Niño. For example, market squid, which typically move north in warm conditions, have been following the squid along the Oregon and Washington coasts. Meanwhile, red crabs, which are usually found off Baja California, have been seen along the West Coast but not in the large numbers typically seen during El Niño events, suggesting that the full influence of El Niño has not yet arrived. Seabird populations are also under observation, as their health and numbers reflect the availability of their prey. Early signs indicate that conditions remain poor for pelicans and Brandt's cormorants, similar to what was seen during the 2015–2016 El Niño, when many seabirds in the California Current experienced population declines and even reproductive failure. Another indicator is the diversity of copepod species near Newport, Oregon. A higher diversity of copepods suggests water has traveled farther, a common sign during El Niño. These conditions are generally not favorable for salmon, as the copepods have less lipids, which are crucial for young salmon to grow when they first enter the ocean.