Algae is a building and terrain type exclusive to the Cymanti tribe, replacing the Port, that allows land units to walk on water and ocean tiles. It produces 1 population for the city it is built in. The Clathrus building produces 1 star per turn for each adjacent Algae. Algae can also be created when a poisoned unit dies on a water or ocean tile.
Almost all units' movement speed is slowed to 1 when moving on algae, except for the Centipede, Hexapod, Raychi, Doomux and any flying units.
Units that can move exclusively on water can still move on algae, but they receive a movement penalty.
Units that move faster on ice do not move faster on frozen algae. They're still slowed.