Queen Isabella Causeway, Road bridge in Port Isabel, Texas, United States.

The Queen Isabella Causeway is a road bridge in southern Cameron County, Texas, linking Port Isabel to South Padre Island. It spans the Laguna Madre for 2.37 miles (3.8 kilometers) and carries traffic as well as utility lines for electricity and fresh water.

In September 2001, loaded barges collided with a support column, causing two sections of the bridge to collapse and killing eight people. Following the accident, engineers installed a fiber optic warning system to monitor the structural condition.

The bridge is named after Queen Isabella of Castile. It was renamed the Queen Isabella Memorial Bridge two years after reopening, in memory of the eight people killed in the 2001 collapse. The earlier causeway's central section became the Queen Isabella State Fishing Pier.

The bridge is the only road connection to the island and is used daily by locals and visitors heading to the beaches. Winds over the water can be strong, so drivers should take care, especially in tall vehicles.

The warning system installed after the 2001 collapse is a fiber optic system costing $900,000, designed to signal a collapse rather than to monitor structural stress continuously. The bridge also carries electricity lines and fresh water to South Padre Island, so the roadway doubles as the island's utility lifeline.