They are surfing.
They are kayaking.
swim
surf
He's windsurfing
He's waterskiing.
He isn't waterskiing.
kayak
sail
sail
surf
snorkel
dive
He is swimming
He is swiming.
They is sailing.
They are sailing.
They are sail.
dive
snorkel
waterski
windsurf
surf
snorkel
windsurf
waterski
She is snorkeling.
She is snorkel.
She are snorkeling.