Anchialine pools are rare and localized brackish-water systems fed by a mixture of groundwater and seawater (with no direct surface connection to the ocean). This unusual aquatic ecosystem occurs in few places in the world, including the coastline of many Hawaiian islands.  These systems support a unique crustacean and mollusc fauna, many of which are candidates for listing as endangered species.  We have conducted baseline surveys of pools in four National Parks on the Island of Hawaii, and are developing a classification scheme based on pool structural origin, size, age, water chemistry, substrate, and vegetation type.  A range of pool types occur in the National Parks, from walled fishponds to undisturbed pools in collapsed lava tubes, cracks, and caves.  Species identified during reconnaissance surveys to locate pools include the crustaceans Metabetaeus lohena and Halocaridina rubra, the mollusc Neritilia hawaiiensis, and the damselfly Megalagrion xanthomelas.  Anchialine pools are threatened by numerous anthropogenic activities, a few of which include introduced fish (tilapia and poeciliids), upstream and adjacent development, and ground-water pumping.  A monitoring protocol is being implemented by the National Park Service Inventory and Monitoring Program to allow assessment of pool status and to evaluate restoration potential.