Place almost any land tower on water with the Pontoon! Deploy the Pontoon on water, then place your land tower on top.
Official BTD5 and BTD6 Description
The Pontoon is a Special Agent that was released on May 17, 2012 on Bloons TD 5, and also appears in Bloons TD 6. It allows all land towers to be placed on water and costs 40. It costs 50 in BTD6.
Pontoon Pro gives towers a range boost. Players need 50 Pontoons to unlock it, which costs 2,000. This is only available on BTD5 Flash and BTD5 Mobile/Steam/Console.
You can't sell the pontoon until you sell the towers on top of it first.
In BTD5 Mobile, a Banana Farm can not fit on a pontoon, due to its large footprint.
This is one of the cheapest Special Agents (the others being Portable Lake and Monkey Farmer) costing 40.
This is one of the few Special Agents that never attacks.
The Pontoon is not sacrificed by the Temple of the Monkey God. It will also collapse and destroy itself if a TotMG is built on to of it, also collapsing the Temple as well.
An Avatar of the Vengeful Monkey on top of a Pontoon.
Some say that the Portable Lake is better because the Portable Lake is helpful on many tracks with more land while the Pontoon is only helpful on tracks filled with water like Archipelago or Spice Islands, but others would debate that Portable Lakes are only for the use of Monkey Buccaneers and/or Monkey Sub, making them virtually useless.
It is possible to place a Pontoon on a Portable Lake but this is worthless and wastes 80/40 if you spent it on Monkey Money.
When placing a Pontoon Pro on a Portable Lake or Portable Lake Pro though, it becomes pretty useful.
The player cannot place a Pontoon on a Portable Lake in BTD6.
The art of the Pontoon has an inflatable tube underneath the Pontoon (probably because the Pontoon doesn't have enough buoyancy on its own to carry towers).
Strangely, the Pontoon has a pop count, even though it cannot attack.
In BTD6, selling a Pontoon or Portable Lake will also sell the towers on top of them.