Venomous eels with shaggy scales that resemble seaweed

Weed Eels are a specific variety of venomous eels which have excellent natural camouflage; indeed, a group of weed eels looks very much like a bunch of seaweed due to their "shaggy" scales and coloration. An individual weed eel is around 5 feet long and weighs about 300 pounds. Colonies of weed eels live in chaotic networks of tunnels with multiple "holes" or entrances arranged in clusters, and by extending themselves from these holes they complete the illusion of being just a patch of weeds.

Found in both salt and fresh water, preferring depths of around 30-ft

Weed eels are found in both salt and fresh water, preferring depths of around 30-ft. Weed eels are so-called because of their brownish green colouration, and because they tend to anchor themselves in the rocks and dirt of the sea or lake bed, looking for all the world like a bed of sea weed. Weed eels have a single biting attack which injects a powerful poison into the wound: the victim must save or die. A weed eel lair consists of many small tunnels of about 6 inches diameter which eventually join into a series of 6-ft tunnels, which in turn lead to a large cave which is the actual lair. The cave is usually about 600 square-ft and the eels pave the bottom of it with any suitable material they find: small stones, gems, coins, and similar sized shiny objects. Any attempt by anyone or anything other than a weed eel to enter any hole leading to the lair will provoke an immediate attack by every eel in the colony. Treasure: None carried. In lair: 1d4×1,000 cp (30%), 1d10×1,000 sp (50%), 1d3×1,000 ep (20%), 1d8×1,000 gp (45%), 2d8×100 pp (60%), 6d6 gems (50%), 2d6 jewellery 50%