Taam Ja' blue hole is an underwater sinkhole located in Chetumal Bay at the southeast corner of the Yucatán Peninsula. Its name means deep water in the Mayan language and, at over 420 metres (1,380 ft) deep, it is the deepest known blue hole.

Blue holes generate a distinctive blue color when seen from above and are typically only a few dozen meters deep.

It was discovered in about 2003 by a local diver who followed a grouper that went into its mouth. The hole was forgotten until the son of that fisherman began working with marine academic Juan Carlos Alcérreca-Huerta, who took soundings of its depth and was surprised by the results.

The mouth of the hole is nearly circular, with a major axis measuring 151.8 metres (498 ft), oriented about 10.76 degrees clockwise from North – similarly to the orientation of major faults in the area.