Some Fun Facts according to Wikipedia:
A study was conducted during one of the Mirror Lake Jumps where water samples were taken from the lake throughout the night. It was note worthy that the ammonia levels in the lake greatly increased throughout the night. This has been attributed to people urinating in the lake. There has also been concern that the lake may be a potential source for disease infection, salmonella is a concern. The Ohio State University usually spends approximately $20,000.00 cleaning up the landscape and property surrounding Mirror Lake after the jump event. Jumping into Mirror Lake is also a fourth-degree misdemeanor.A notable non-Michigan game jump occurred on the night of May 1, 2011, when students jumped into the lake in spontaneous showing of patriotism in the wake of the death of Osama bin Laden, announced on television at approximately 11:30 pm.
It should also be noted that there are much better videos of the Mirror Lake Jump if you search for them on YouTube, however they might not be suitable for young children and thus not suitable for my blog!