shoal

shoal \shohl\, noun:

1. a place where a sea, river, or other body of water is shallow.
2. a sandbank or sand bar in the bed of a body of water, especially one that is exposed above the surface of the water at low tide.

adjective:
1. of little depth, as water; shallow.

verb:
1. to become shallow or more shallow.
2. to cause to become shallow.
3. Nautical. to sail so as to lessen the depth of (the water under a vessel).

A few minutes later Tom was in the shoal water of the bar, wading toward the Illinois shore. Before the depth reached his middle he was half way over; the current would permit no more wading, now, so he struck out confidently to swim the remaining hundred yards.
-- Mark Twain, The Adventures of Tom Sawyer, 1876

That piece of land is permeated with a perfect shoal of mineral springs.
-- Ada Clare, Only a Woman's Heart, 1886

Shoal comes from the Old English term sceald meaning "shallow." It was spelled with a d up until the 1500s.