In May the Towy has a run of the rare and protected twaite shad and allis shad. The Towy also contains brown trout, eels, pike, and a variety of small fish species, and is home to brook lampreys, river lampreys and sea lampreys.

The Towy has the distinction of having accidentally produced by far the biggest fish ever taken on rod and line in fresh water in Britain. This was a sturgeon (Acipwienser sturio) weighing 388 lb (176 kg)