Stingrays are not dangerous unless they feel threatened. Here's some information on how to scuba dive with them safely, and first aid for stings. read more
There are aquariums that you can go to that have sting rays and have their barbs removed. They are very interesting to touch. Not all eels are harmful. Electric eels can transmit a voltage of up to 800+, though and yes, can be very deadly to humans. read more
Irwin was swimming with one of the larger species of rays out there -- Australian bull rays can be up to 4 feet (1.2 meters) wide and 8 feet (2.4 meters) long -- but all stingrays use the same attack mechanism regardless of size. The mechanism is called a sting, up to 8 inches (20 cm) long in a bull ray, located near the base of the tail. read more