 On average , the system is 3 meters ( 9 @.@ 8 ft ) deep , and covers approximately 497 square kilometers ( 192 sq mi ) . It is the fourth largest estuarine system in Texas behind Galveston Bay , <unk> <unk> and Matagorda Bay . The two main extensions are : Nueces Bay , which extends west to the mouth of the Nueces River , and Oso Bay , which extends south to the mouth of Oso Creek . Every second , approximately 34 cubic meters ( 9 @,@ 000 U.S. gal ) of water flows into the bay . The exchange with the Gulf of Mexico occurs at Aransas Pass . As a result of the seawater exchange , the bay 's salinity is 22 parts per thousand ( <unk> ) , which is lower than the seawater average of 35 <unk> . 
