Lough Derg is famed for its Brown Trout fishing, particularly during the Mayfly season which tends to peak in mid-May. Trout feed voraciously on the Mayfly before heading upriver to spawn. The lake is also teeming with coarse fish including Pike Perch, Roach, and Bream. There once was a commercial Eel fishery on Lough Derg but Eels are now protected due to the drastic decline in their numbers within the European Union. Pollan, a rare type of fish, is also present in the lake although numbers are much reduced. Pollan is only found in five Irish lakes - its nearest relatives are in the arctic. The lake contains a landlocked population of Sea Lamprey, River Lamprey, and probably some Brook Lamprey. Lamprey is a primitive and peculiar group of fishes that look like eels. Some attach themselves to other fish during their lifecycle.