Firefighting planes are dropping ocean water during the Los Angeles wildfires – which is why using salt water is usually a last resort

The efforts of firefighters battling the deadly wildfires that swept through the Los Angeles area in January 2025 were hampered by limited supply of fresh water. So, when the winds are composed enough, qualified pilots fly the planes aptly named Super Scoopers If collecting 1,500 gallons of seawater at once and throwing them into the fires with great precision.

Using seawater to extinguish fires may seem like a straightforward solution – the Pacific Ocean has seemingly unlimited water resources. In emergency situations like southern California, this is often the only quick solution, although surgery may be an option risky among the ocean waves.

But seawater also has disadvantages.

Maritime causes corrosion of fire extinguishing equipment and can harm ecosystems, especially such as the chaparral bushes around Los Angeles, which are not usually exposed to seawater. Gardeners know that compact amounts of salt – added as fertilizer, for example – do not harm plants, but too much salt can stress and kill plants.

While the consequences of adding seawater to ecosystems are not yet well understood, we can gain insight into what to expect when considering the effects of sea level rise.

Experiment with sea water in a seaside forest

as ecosystem ecologist at the Smithsonian Environmental Research Center I run a an innovative experiment called TEMPEST this was intended to understand how and why historically salt-free coastal forests respond to their first contact with salt water.

Sea level rise increased average o about 8 inches over the last century around the world, and this water has pushed saltwater into American forests, farms and neighborhoods that previously only knew freshwater. As sea level rise accelerates, storms push seawater further and further onto dehydrated land, ultimately causing trees to die and ghost forests to form – as a result of widespread climate change in the US and around the world.

in ours TEMPEST test plotswe pump salty water from the nearby Chesapeake Bay into tanks and then spray it on the forest soil surface quickly enough to saturate the soil for about 10 hours. This simulates the surge of salt water during a enormous storm.

Our coastal forest showed little impact after its first 10-hour exposure to saltwater in June 2022 and grew normally for the rest of the year. In June 2023, we increased the exposure to 20 hours and the forest still seemed mostly undisturbed, although tulip poplars They took up water more slowly from the soil, which may be an early warning sign.

The situation changed after a 30-hour exposure in June 2024. Tulip poplar leaves in the forests began to turn brown in mid-August, a few weeks earlier than usual. In mid-September the forest canopy was bare, as if winter had come. These changes did not occur in a nearby plot, which we treated in the same way, but with freshwater rather than seawater.

The initial resilience of our forest can be partly explained by the relatively low salt content of the water in this estuary, where water from freshwater rivers and the salty ocean mix. The rain that fell after the experiments in 2022 and 2023 washed the salts from the soil.

However, after the 2024 experiment, there was a severe drought, so the salts remained in the soil at that time. The trees’ prolonged exposure to salty soils after our 2024 experiment may have exceeded their ability to tolerate these conditions.

The seawater released by the Southern California wildfires is full-strength salty ocean water. The conditions there are very dehydrated, especially compared to our forest plot on the east coast.

Changes noticeable in the substrate

Our research group is still trying to understand all the factors that limit a forest’s saltwater tolerance and how our results apply to other ecosystems like the one in the Los Angeles area.

The leaves of the trees turning from green to brown well before fall were a surprise, but there were other surprises hidden in the ground beneath our feet.

Rainwater seeping through the soil is usually clear, but about a month after the first and just 10-hour exposure to saltwater in 2022, the soil water turned brown and stayed that way for two years. The brown color comes from carbon-based compounds leached from dead plant material. It is a process similar to brewing tea.

Our laboratory experiments suggest that the salt caused the clay and other particles to disperse and move through the soil. These changes in soil chemistry and structure can persist for many years.

Sea level rise increases coastal exposure

While ocean water can aid fight wildfires, fire officials have reasons for doing so they prefer fresh water sources – provided fresh water is available.

Meanwhile, U.S. coastlines are facing increasing and more constant exposure to saltwater as rising global temperatures accelerate sea level rise, which is submerging forests, fields and farms, creating unknown threats to coastal landscapes.