[n] a large group of fish; "a school of small glittering fish swam by"
[n] a stretch of shallow water
[n] a sandbank in a stretch of water that is visible at low tide
[adj] full of submerged reefs or sandbanks or shoals; "reefy shallows"; "shoaly waters"
[v] become shallow; "the lake shallowed over time"
[v] make shallow; "The silt shallowed the canal"