Nicole Eggert -- PHOTOS Of Gruesome Diving Injuries ... In a Thong

THE BAD NEWS: Nicole Eggert suffered gnarly injuries as a result of her failed high-dive on the set of "Splash" -- her entire backside was battered and bruised as the pictures so vividly show.

We broke the story ... the "Baywatch" star was filming the finale and attempted multiple back flips and landed squarely on her backside. EMTs helped her out of the pool and she was taken to the hospital.

The bruising was so severe, Nicole was tested for kidney damage. So far so good.