Spillway is a toxic waste dump with four bloon paths, each coming from the four corners. Bloons enter around the toxic pool and then exit on the opposite path that they entered from.
In the middle of the toxic waste pool, there is a metal barrel where only one small footprint tower (Dart Monkey, Tack Shooter, Ice Monkey, Glue Gunner, Sniper Monkey, Ninja Monkey, and Alchemist) can be placed on.
On the outside, there is concrete floor with a bunch of contaminated gas masks, bottles of toxic fluid, and a contaminated lab coat.
There are four inflatable walls on each side of the toxic waste pool that can be removed for $2000 each. When removed, a visual Engineer Monkey will blowtorch out the edges of the inflatable wall, and the inflatable wall falls into the toxic waste.
- Main article: Spillway/Strategies
- This is the first map to have obstacles that cost more than $1500 per obstacle.
- Due to an error when adding the map decorations for the Independence Day Collection Event on version 18.1, the map instantly caused the game to crash upon loading while the event was active. As a result, it was also disabled on co-op, and attempting to start a co-op game on Spillway will result in an error.
- This was fixed as of Version 19.0. Interestingly enough, there were two days left for the event.
- It is possible to let a 0-2-0 Tack Shooter attack from the barrel if it is placed pixel-perfectly at the lowest point of the barrel.
- The hazmat masks appear to be the mask the Bloon Dissolver is wearing, and in the bottom appears to be the glue gun from the Bloon Solver.