The die-off has been massive. Over 100,000 dead fish began turning up in the Mississippi River delta earlier this week and have since formed a carpet on some parts of the bayou. The area affected by the die-off had previously been polluted by the BP oil spill in the summer, leading scientists to initially suspect a connection. Experts have since determined it was caused by rising water temperatures resulting in lower oxygen levels in combination with a low tide which essentially trapped the fish.