Green/Yellow/Black Floating Algae

[Bluesky]

I have had a 55gal freshwater tank for six years and suddenly I have a huge algae bloom (?) of floating bright yellow, green and black algae that is slimy and foamy. It clings to the tops of the large plastic plants that float to the top of the water. What is this stuff, why is it suddenly here, and how do I get rid of it? The only change recently was the addition of a large piece of African root driftwood purchased from Petco.