The climate in the region of the Island is extremely hot and
arid, with average annual rainfall of 2.4 in (60 mm). Montague Island, as part of the Colorado river delta, has had its ecology radically altered by diversion and use of water upstream in the river. The only water reaching the delta, with the exception of occasional floods, is
agricultural wastewater. At least seven species of water birds are known to breed on Montague Island. The island is one of two known active breeding colonies of
elegant tern in Mexico. During two years, a large number of nests were destroyed by
tidal flooding, but there were only low levels of nests lost to
predation. The birds nesting on Montague Island have reacted strongly to
El Niño, with
brown boobies being replaced by
blue-footed boobies, and an increase in nesting of least, elegant, and royal terns, as well as
black skimmers. Montague Island is one of the few locations where
Mulinia coloradoensis, an endangered species of
clam, is found. This species was once extremely abundant near the mouth of the Colorado river, but now only exists in a few isolated places. The decline of this clam is explained by the increase in salinity of the water due to diversion of and use of water from the Colorado river. ==Energy resources==