River Tywi these fish to over in weight. In summer and autumn there is also a substantial run of Atlantic salmon ("Salmo salar"). In May the Tywi has a run of the rare and protected twaite shad ("Alosa fallax") and allis shad ("Alosa alosa"). The Tywi 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 Tywi 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
Coonamesset River while environmental awareness has increased, bringing the conservation goal to the fore. While the Coonamessett maintained a healthy herring run for many years alongside Cranberry cultivation, in recent years the herring run has undergone a massive decline, following a similar decrease across New England which has been widely attributed to at-sea factors external to the rivers. In 2004, fish counters saw only 640 fish and the only about 2000 herring returned to spawn. Concern over the herring run and the disappearance of sea run trout has led to a consensus in the Town for better protection and improvement of the