For as long as people have sailed the seas there have been stories of terrible sea monsters. Here are 30 detailed illustrations that portray such real monsters as the giant squid, double-crested crocodile, and great white shark, as well as more fanciful beasts: the tusked pig whale, the Bardfysshe, Loch Ness monster, and more. Dover Original.
Here's a sample of other books in this Dover category
Mythical Beasts Coloring Book by Fridolf Johnson Thirty handsome drawings of fabled creatures: mermaid, centaur, phoenix, basilisk, kraken (a huge sea monster sometimes mistaken for an island), manticore (a beast of three different parts), and more.
Shipwrecks and Sunken Treasures Coloring Book by Peter F. Copeland 39 accurately detailed illustrations: divers on site of ancient Greek shipwreck, remains of 9th-century Viking ship, German U-boat sinking English freighter (1917), more. Captions included.