Algal Cave (West Tunnel Cave) in the McDonald Creek drainage of Glacier National Park was visited in September 1999 to confirm the presence of cave isopods that had been reported in the cave in 1998, and to collect vouchers if the isopods were observed. Several aquatic cave invertebrates were reported and collected in the cave in 1977, but apparently these had never been identified, and location of specimens was uncertain. Six "pools" in the cave were checked for the presence of invertebrates during the September 1999 trip. White isopods were found in all of the pools; estimated number of individuals in these pools was >800. In addition, a species of aquatic amphipod, at least one species of planaria, and one species of oligochaete worm were present. Vouchers of each species were collected for later determination by experts. The isopod was identified as Salmasellus steganothrix, the amphipod was identified as a new and as yet undescribed species of Stygobromus (to be named "glacialis"), the planaria were not identifiable because of the preservation technique. To date, the oligochaete worm has been identified to the family Lumbriculidae. The aquatic community of cave invertebrates in Algal Cave is the first described for Montana; a similar community may be present in "Zoo Cave", also in the Park, as well as other caves in northwestern Montana with subterranean streams.