This chemical-carrying rainwater is often called runoff. On farms, the pesticides used to treat crops and the waste (poop) from cows can wash into the rivers as runoff and poison not only the fish but also wild animals that live near the water and plants that grow there.
This might not sound like a problem in Santiago (after all, most wild animals don't live in the city), but all the chemicals that wash into the river here will eventually find their way to other places, including the ocean. The best way to prevent this is simply to use fewer harmful chemicals, like fertilizer for the lawn or strong cleaning products, especially outside the house. These are simple steps that you can take to protect the environment no matter where you live. In a city like Santiago, it is also especially important to reduce air pollution because, thanks to the rain, the exhaust from your car can end up in the river, too.
The air may seem cleaner after a rainstorm, but that doesn't mean the pollution is gone for good!
