Didn't find much, on Ambergriscaye.com I found this one:

Originally Posted by Ambergriscaye.com
Adjacent New Haven Lagoon is considered the best deep water harbour south of Placencia. The area features an extensive series of storm ridges and intervening ponding areas, the only such occurrence on such a scale in Belize, derived from sediment discharged by Monkey River, just to the north of the park.


This is a nice Google-composed-search-engine-page on New Haven Belize:

Live and let live