The allies (the RAF) had fairly specialized bombs in WWII to blow dams. They would fly in from upstream and drop a bomb shaped like a barrel (picture a barrel of oil) from very low altitude. The bomb would skip along the surface as it lost momentum and then sink close to the dam wall. At a certain pressure it would blow and take advantage of the hydrostatic shock to break up the wall.

See: https://en.wikipedia.org/wiki/Operation_Chastise

They were trying to do something completely different, with different limitations than Islamic State has. They can get a few operatives up to the dam and place the explosives, but they probably don't have access to planes or the ability to build such specialized bombs.

"Bouncing Bettys"

That's slang for a jumping anti-personnel mine

Yes, they are also called that. I think the dam-buster bombs had the nickname first.