“Bank” is the most common collective noun for monitor lizards, and it points straight at their habitat preferences. Many monitor species, including Nile monitors and water monitors, are strongly tied to rivers, lakes, and wetlands, and riverbanks in particular offer everything they need: basking sun, easy water access, and a steady supply of prey like fish, crabs, and eggs.
Monitor lizards are the largest lizards on Earth, a family that includes the Komodo dragon, and despite their size and reputation as solitary hunters, good habitat can concentrate several individuals along the same stretch of bank without much direct interaction between them. Each one is typically hunting and basking on its own terms, just sharing a valuable piece of real estate.
Monitors are also unusually intelligent among reptiles, capable of problem-solving and even basic counting in some studied species, which makes their loosely shared riverbank territories a bit more layered than simple habitat overlap.
Example: “A bank of monitors patrolled the muddy shoreline, each one working its own stretch of water.”
Related: Collective Nouns for Reptiles · What Is a Group of Monitors Called?