4 week old chick dead. What happened?

[K7S10]

I have 29 chicks (had 30, but a small one died at 4-5 days old).
They are Rhode Island Reds and Shaver Reds.
They're all doing great. Fluttering, perching on me, gobbling feed and even starting to catch a worm or two when they're outside for short periods on nice sunny days.
Just now I went to feed them, and found one of the Rhode Island Red chicks dead by the water dish. I found no scratches or marks on it. There's no diarrhea. It was one of the larger ones too.
They still have the heat lamp (which I turn off of hot days or it gets too hot.) They have plenty of feed and water available.
They'll be 4 weeks old tomorrow.
Any ideas as to what could have gone wrong? HELP!?

 

[Harley's girl]

Was she wet? If so she was probably drinking and another chick stepped on her and drown her.

It sad. I have had that happen to so many chicks now I leave the marbles in the waterer until they are outside full time. But that is just me. Good luck.

 

[K7S10]

No, the chick wasn't wet at all. The waterer is raised up on a couple of bricks so that they stop getting the shavings in it. I did put marbles in the waterer for the first 2-3 weeks.

Here's a pic of one of the Rhode Island chicks taken several days ago. The one that died was even bigger.

Well. I'm just hoping that it's nothing contagious.

 

[Harley's girl]

Sometimes they do that. You got yourself a real nice looking roo there! Ironically enough.....I had a chick drown today in the waterer.

 

[K7S10]

Awww. Sorry to hear that.
*UPDATE* Found some bloody poo in the coop today. What's causing that?