Welcome to Camp Nightmare (Goosebumps Presents #3) by Megan Stine, Jeff Cohen , R.L. Stine

"When I first got to Camp Nightmoon, I thought it was a pretty cool place. They had basketball, archery, and a really big lake. But then all this weird stuff started happening.
"First Mike got bit by a snake. And Roger was attacked by a creature in the woods. Then yesterday, Jay and Colin disappeared in the lake. Can you believe it? Guys are dropping like flies. And I'm afraid I'm next!"
-Billy Harlan