A rising number of sea lions are being poisoned by toxic algae blooms in California, according to The Associated Press. So far, 68 sea lions have been treated by the Marine Mammal Center in Sausalito, compared to 70 in all of 2016. The number "is more pronounced than we've seen in the past few years,” Michael Milstein, a spokesman for National Oceanic and Atmospheric Administration, told the AP.

The sea lions are getting sick because they eat small fish like sardines and anchovies that feed on the toxic algae. (The fish apparently don’t get ill.) The algae release a toxin called domoic acid, which affects the brain, and can harm and even kill humans when contaminated shellfish is consumed. Most of the sea lions are being rescued off the Central Coast, which spans from north of Los Angeles to south of San Francisco. But domoic acid levels are increasing and moving further north, according to the AP.

“It's really hard to watch these animals suffer.”

Algal blooms are caused by the industrial and agricultural runoff of nutrients like nitrogen into rivers and coastal waters. Nitrogen is food for tiny algae — and when it’s washed ashore, it can feed algal blooms. Not all blooms are toxic, but they still create big damages: runoff from the Mississippi River is causing the biggest dead zone ever recorded — as large as New Jersey — in the Gulf of Mexico, for instance. That’s because when those algae die, they sink to the bottom and decay, using up oxygen in the process. This creates areas of low oxygen where fish and shellfish can’t survive.

Climate change is only going to make the problem worse: warming ocean waters boost the growth of the tiny algae, and more rain and more extreme storms in the future will wash out increasing amounts of nutrients into waterways. This is bad not only for animals like the sea lions that are being poisoned in California, but also for water quality and business. Algae blooms have shut down fisheries before and cut drinking water supplies.

As for the sea lions, ingesting domoic acid can cause brain damage and seizures, and ultimately death. "It's hard,” Cara Field with the Marine Mammal Center told CBS News. “It's really hard to watch these animals suffer, especially if there's not something we can do to stop these blooms from happening.”