Deep Hole is a karst sink located in Myakka River State Park, Sarasota County, Florida.
Lake levels exhibit pronounced depth variation from wet to dry season and Deep Hole is a refuge for wildlife during the dry season. Prior studies of river rocks estimated the age of the Myakka River basin at several million years although the formation period for Deep Hole is unknown.
Notably, evidence for one of the earliest documented human settlements in the area now defined as the United States occurs within the Myakka River basin from two sinkhole features, Warm Mineral Springs (WMS) and Little Salt Spring (LSS) which yielded artifacts that have established human habitation in the area to 10,000 – 12,000 years before present.
The authors collaborated to compile existing information and conduct preliminary investigations of water quality and underwater topography. Water quality data were collected in August 2011 and in April 2012 a technical dive team explored the sink to determine the overall depth and document similarities to WMS and LSS, and offshore submarine springs.
Unique characteristics of the site necessitated planning for unknown depth, potential caves, poor visibility and a large number of adult alligators. Findings showed the maximum depth to be 41 m for ambient dry season lake levels, no significant ledges or caves were found. There was a strong thermocline at approximately 9 m in August 2011 and 6 m in April 2012 below which the water was anoxic.
For the August visit water temperature was uniformly 14.2 degrees C below 12 m, colder than the typical approximately 22.5 degrees C for Florida spring water indicating the sink does not have underlying spring flow. Long-term temperature records indicated there is some seasonal warming near the thermocline. Water quality parameters varied with the temperature stratification and were dissimilar to Warm Mineral Springs and Little Salt Spring where warm, mineralized water rises from a deep aquifer.