While people generally associate dolphins with the world's oceans, there are a few species that can be found in rivers and brackish waters. Several are in South Asia, while the only river dolphins in the Western Hemisphere live in South America, specifically the Orinoco and Amazon rivers. Not all of the Amazon's pink dolphins are, in fact, pink; younger dolphins tend to be gray. Males are typically pinker than females as the distinctive hue is caused by skin abrasions, and more aggressive males tend to accumulate more scratches over the course of their lives than female dolphins do. These pink dolphins are endangered, largely due to habitat loss and increases in the levels of various toxins in the Amazon.