By far one of the coolest things to do in Parguera is tour through the man-made mangrove channels. These channels were cut years ago, and local fishermen would use them to protect themselves from storms as they made their way back to the marina. I enjoy the longer and shorter channels and would recommend hiring a knowledgable captain for the day to take you through both if you prefer to travel by boat.
If you are adventurous and have the endurance, take off in a kayak from the marina and head west. You'll find a maze of channels and just enjoy exploring on your own time.
Don't get out into the water, as many mangrove and seagrass beds hide "upside down jellyfish" which sit innocently on the bottom unless disturbed by excessive water motion. Just a heads-up!