A fish that is a great favorite with people is the salmon. It begins its life in a small pool up a river. Far from the sea, the fish lays its eggs in a pool in the river. When the baby fish are a few inches long, they begin to swim down the river. As they grow bigger, they make their way towards the sea. They jump over rocks, often with their tails first. Suddenly, they find themselves in the sea. The fish live in the sea for three years. They swim far away from land. How do they find their way back? These fish have a wonderful sense of smell. They always remember the smell of their journey to the sea easily, because the river was flowing to the sea and carried them there. Most of them live and keep swimming towards pools. As soon as they reach a pool, the females lay their eggs. They lay their eggs near the edge of the water and cover them with sand. Soon the eggs hatch and the pool is full of small fish, getting ready for the long journey out to the sea.

Which detail explains how fish find their way back home?