Sinking pools are obstacles in the early games in the Sonic the Hedgehog series which first appeared in Sonic the Hedgehog 2. If a playable character stands in these pools for too long, it will cost the player a life.
The sinking pool are pools of quicksand, oil, or other liquids in the Zones which the playable characters gradually sink into in a manner of seconds and will cost the player a life, regardless of Rings, similar to how the player falls into a bottomless pit. The difference however, is that the player can in general jump continuously in the sinking pools to stay above their surface and cross them.
Sonic the Hedgehog 2
The sinking pools' first appearance was in Sonic the Hedgehog 2, where they are featured in Oil Ocean Zone. Here, the bottom of the entire Zone is flooded in thick crude oil that serve as the sinking pools. It is possible to skim across the entire Zone by Spin Dashing across the oil, but it requires very good timing; this feature has been removed in the remake.
Sonic the Hedgehog 3 & Knuckles
In Sonic & Knuckles, there are quicksand pits throughout Sandopolis Zone. Most of them serve as sinking pools that will drown the playable character. Others however, have secret areas underneath them that can be accessed if the player let themselves sink into them. The Guardian is as well defeated by luring it into or knocking it into a quicksand pit.
Sonic Adventure 2
In Sonic Adventure 2 and its remake Sonic Adventure 2: Battle, Hidden Base and Sand Ocean have quicksand fields. However, should the playable characters, Tails and Dr. Eggman respectively, fall into these quicksand pits, they will be unable to leap out of the quicksand due to both of them using a heavy walking mech, although they will still slowly sink into it, resulting in an instant loss of life. On the other hand, during the battle against the Egg Golem, if Sonic falls into the quicksand pit at the bottom, he can repeatedly jump to avoid sinking to his doom, and grab onto one of the pulleys to return to the upper area; if Eggman slips into the same pit during his fight against the Egg Golem, then he would sink to certain doom.
- The quicksand sections of Oil Desert Zone in Sonic the Hedgehog 4: Episode II will not take a life from the player when the playable characters sink into them, but instead slow the player down.