A 2016 expansion of the Panama Canal helped bigger ships move through the waterway. But it created an unintended side effect: saltwater fish from both oceans are now swimming into the canal's main freshwater lake, pushing out local species and threatening nearby communities, reported the New York Times.What's happening?Scientists at the Smithsonian Tropical Research Institute found that fish from the Atlantic and Pacific — including snooks, jacks, and snappers — have dramatically increased in Lake Gatún since the canal's expansion. These ocean species are replacing peacock bass and tilapia, two freshwater fish that local people rely on for food.The changes affect people like Félix Martínez González, who fishes Lake Gatún in his powder blue canoe.AdvertisementAdvertisementAdvertisement"I'm not worried for myself; I'm worried for the next generation," he said. "All this affects them, too." On a recent day, he caught only 16 pounds of fish in six hours — half his usual catch before the expansion.Local fishing guide Oswaldo Alberto Robles sees the impact on sport fishing, too. "Imagine 20, 30, 40 boats searching for one fish," he said. "We'll just keep running out of them even faster."Why is this fish invasion concerning?The problem goes beyond fewer fish for dinner. Scientists worry that some species, like the venomous lionfish from the Caribbean, could swim through to the Pacific Ocean and harm fish populations there. The canal's rising salt levels also threaten half of Panama's drinking water.Watch now: Giant snails invading New York City?Manuel Cheng Peñalba, a member of Panama's legislature, points out nobody discussed salt problems before expanding the canal. Now, people worry about water access in one of Earth's rainiest countries.What's being done about the fish invasion?Panama's leaders say they're working on solutions. Juan Carlos Navarro, the environment minister, used a Spanish saying to describe their approach: "I get dressed slowly because I'm in a hurry" — meaning they'll act urgently but carefully.AdvertisementAdvertisementAdvertisementScientists think adding barriers like electric fields or air bubble curtains might block some fish. But these fixes could slow down ships. And with invasive species, results are hard to predict.Do you think America does a good job of protecting its natural beauty?DefinitelyOnly in some areasNo wayI'm not sureClick your choice to see results and speak your mind.Dr. Bella Galil, who studies similar issues in the Suez Canal, said controlling unwanted species takes time. "It takes a lifetime," she said. "But if you don't start, you are left with a destroyed sea."Join our free newsletter for good news and useful tips, and don't miss this cool list of easy ways to help yourself while helping the planet.