The Middle Island Sink Hole is situated 100' north of Middle Island, 3 miles out of Rock Port.
The bottom near the island is composed of sheets of lime stone which step down to 22' before falling into the sink 50 some feet below.
The major out flow historically has been at 75' deep in the southeast corner, at the bottom of the wall.
This area I have reffered to as "The Crater" which resembles an impact crater with a verticle wall to it's south.
Going up and over the north rim you will find both purple and white algae.
The white is usually growing in concentrations near higher flow areas, where the purple forms a carpet for the rim.
Here is where you are most likely to expirence the halocline between the much warmer lake waters and the fourty something springs.
It can be just some fuzzy viz like above a hot desert road or a cloud bank.
The Spring water has a yellowish tint to it due to the higher sulpher content of the springs.
In the last 5 years a crack with a flow has opened up on the west side of the sink near the NOAA buoy. To the north is a rubble field without much of a relief. If lead is what your after, the east side is where to look. Follow the many down rigger cables to their ends and see if others have beaten you to the cannon ball yet. The central area is a 300' wide plain of "suspended solids." A bottom finder will tell you it's up to 15' thick in spots, so do not decend into this zero viz enviroment that must be laced with down rigger cable as well.
I guarantee you a memorible dive in Middle Island Sink. And please, bring back pictures for me to post on this web site!