Read the passage below before answering the question. The Mystery of Great Salt Lake High in the desert valley of northern Utah lies the Great Salt Lake, the largest saltwater lake in the Western Hemisphere. Unlike most lakes, the Great Salt Lake has rivers flowing into it—such as the Bear, Weber, and Jordan rivers—but no rivers flowing out. Because water can only leave the lake by evaporating into the air under the hot desert sun, minerals and salts brought by river currents are left behind. Over thousands of years, these minerals accumulated, making the lake up to eight times saltier than the ocean! Because the water is so salty, fish cannot live in the main body of the lake. Instead, billions of tiny brine shrimp and brine flies thrive in the salty water. Millions of migratory birds, including phalaropes and American white pelicans, stop at the lake each year to feed on these tiny creatures before continuing their long flights across North America. What is the main idea of this passage?