Hynes Bay is a shallow coastal bay within the Guadalupe River delta system on the Texas Gulf Coast, located between the towns of Austwell and Seadrift. It is part of the larger Guadalupe estuary, receiving freshwater inflow primarily from the San Antonio and Gualupe rivers. The bay is notably shallow, with an average depth of only three to four feet. A specific public kayak launch site exists in the town of Austwell, providing direct access to Hynes Bay. A known paddling trail runs across the bay from Seadrift to Austwell. The bay's shoreline includes areas of salt marsh, and a portion of the bay's shoreline within Townsend Bayou has been noted for habitat change. The broader area is part of the Guadalupe Delta Wildlife Management Area, with a specific Hynes Bay Unit, though public access for paddling may be subject to permit requirements for entry; visitors 17 and older need an Annual Public Hunting or Limited Public Use Permit to enter the WMA lands.

The bay's character is strongly influenced by wind and tides. The bottom is very soft and unforgiving, which could complicate any attempts to stand or wade from a craft. Wind direction significantly affects water clarity; a hard south wind can muddle the bay, while a north wind is considered preferable. The area is known for abundant birdlife, including seasonal flocks of White-faced Ibis and foraging White-tailed Hawks and Peregrine Falcons, which can be a notable sight for paddlers. Navigational hazards exist, as there are sunken barges and other obstructions in the area that are not always marked on GPS. The bay is part of a complex deltaic estuary ecosystem featuring brackish water, coastal marshes, and corridor forests along the small bayous.