The fish known for its ability to swim upstream to spawn is the salmon. Salmon are renowned for their remarkable life cycle, which begins when they hatch in freshwater rivers. As they mature, they migrate to the ocean, where they feed and grow. When it's time to spawn, adult salmon exhibit a remarkable instinct to return to their birthplace, swimming upstream against strong currents and overcoming significant obstacles. This journey can be perilous, and not all make it back. Their life cycle is a natural marvel and plays a crucial role in the ecosystem, contributing nutrients to both freshwater and marine environments.