Nashua Spring is a fifth-magnitude spring that has an elongated spring pool about 85 feet long and 20 feet wide, situated in a grassy clearing on the east side of the St. Johns River. Flow is from two vents about 50 feet apart near the north side of the pool. The east vent measured 6.5 feet deep and about 3 feet to 4 feet in diameter; the west vent was 8 feet deep and tapered down from 8 feet to 3 feet in diameter. The depth of the rest of the pool was about 2 feet to 3 feet. The spring run is 3 feet to 5 feet wide and flows about 300 feet towards the west to the St. Johns River. The water level in the spring pool is reportedly affected by tides, and the spring is subject to flooding by the river.