Sultan Marsh (Turkey) is one of the largest wetland of the Middle East and Europe. The marsh was designated as a Ramsar Site, a Nature Conservation Area, and recently a National Park by Turkish Government. Despite its strong conservation status, the marsh has undergone rapid degradation in recent years. However, major changes have been observed in Sultan Marsh in the last two decades. The water spider, Argyroneta aquatica (CLERCK, 1757), was lastly observed in 2000 in the region. Since then, this species has not been observed in the marsh. Increased of pollution in Sultan Marsh is the most probable cause for lacking the species. It may be argued that the water spider can be used as an ecological indicator to determine environmental changes.