Mass Fish Deaths: Hundreds of Thousands of Fish Have Died at Popular California Lake in Monterey County Since Last Week

Mass fish deaths, also called fish kills, are events that involve the local die-off of any fish species in an inland body of water or the open sea. For decades, scientists have observed this phenomenon taking place in different parts of the world, including from the Americas to Europe and Asia.

Considered by many as an ecological disaster, fish kill can impact the local ecosystem and environment where they live.

In the United States, mass fish deaths have occurred in recent years such as in Texas and North Carolina. Recently, a fish die-off has been observed at a popular California lake in Monterey County since last week. According to local reports, hundreds of thousands of fish have already died at the Golden State's Lake San Antonio. Scientists suspect the reason behind the deaths is a lack of oxygen.

Based on data from various sources, both natural and anthropogenic factors contribute to fish kill worldwide. In addition to deoxygenation, the other causes of mass fish deaths include excessive fishing, ocean warming or acidification, and marine pollution.

Even larger marine creatures such as sea turtles, whales, and dolphins are not exempted from these life-threatening risks.

What Are Mass Fish Deaths?

Fish die-off is a term used by marine scientists and other experts to pertain to the deaths of a relatively large fish population in a certain area or region.

According to an Australian Government agency, low levels of oxygen in the water is the main cause of mass fish deaths but asserted that it can also be caused by other reasons, as mentioned earlier.

The agency Murray-Darling Basin Authority outlines other phenomena that contribute to fish kill:

• Algal blooms
• Blackwater events
• Entry of acidic water into lakes and rivers
• Fish diseases and infections
• Rapid water quality and temperature changes
• Lack of food resources

California Lake Fish Die-Off

Earlier in July, Monterey County officials warned the public about the ongoing California lake fish die-off. Recently, the California Department of Fish and Wildlife attributed the mass fish deaths to deoxygenation caused by extreme changes in temperature, as cited by local sources. This incident can be compared to other fish kill incidents across the US in recent years.

In 2023, Texas authorities reported that tens of thousands of dead fish washed ashore along the state's Gulf Coast. Officials at Quintana Beach County showed that the dead marine animals were floating in the coastal waters. Authorities concluded that lack of oxygen was the main cause of the Texas fish kill.

Aside from deoxygenation, multiple fish populations are also dying not only from natural causes but also from human activities. In a 2023 study published in the journal Marine Policy, researchers made a conservative estimate that between 24,000 and 32,000 fish die each year over the past 20 years.