Man appears to have been bitten by shark in Texas, authorities say

The man was swimming near a sand bar in the Gulf of Mexico when he felt a tug.

A 42-year-old man has been bitten by what appears to be a shark on a beach in Galveston, Texas, according to local authorities.

The man, who is from Alvin, Texas, about 30 miles away, was bitten above the knee in his right leg around 10 a.m. Thursday, the Galveston County Sheriff's office posted on Facebook.

He was swimming off a sandbar in the Gulf of Mexico near Crystal Beach when he felt a tug in his leg, according to the sheriff's office.

Images released by the sheriff's office show the man's leg covered in deep bite marks.

The man was taken to the the University of Texas Medical Branch at Galveston in stable condition, according to the sheriff's office.

There have been 18 unprovoked shark attacks off the coast in Galveston County, according to the International Shark File, a database kept by the Florida Museum of Natural History.

ABC News' Gina Sunseri contributed to this report.