Lake Worth Lagoon, Lagoon in Palm Beach County, Florida, United States

Lake Worth Lagoon is a brackish lagoon in Palm Beach County, Florida, running parallel to the coast behind barrier beaches such as Palm Beach Island. It is about 21 miles (34 km) long and up to a mile wide, linked to the Atlantic by two man-made inlets: Lake Worth Inlet at the Port of Palm Beach and South Lake Worth Inlet, or Boynton Inlet. Eight causeways and bridges cross it.

This water body was originally a freshwater lake until 1877, when a permanent inlet at Black Rocks connected it to the ocean. This opening fundamentally changed the water from fresh to salty.

The Seminole people called this body of water 'Hypoluxo,' meaning 'water all around, no get out,' reflecting how the water seemed enclosed by land. This name remains part of local geography and history today.

The Intracoastal Waterway runs through this lagoon and handles most boat traffic in the area. Water conditions vary depending on recent rainfall and tidal patterns.

On August 24, 2009, the LagoonKeepers filmed a wide wake moving through the water and called it the "muck monster"; it never broke the surface, and its identity remains unconfirmed. Observers who approached within 10 feet saw it appear to descend deeper.