For those sea-oriented people (like most people who would move to Placencia would normally be, since you have water on both sides of you), you almost feel like you're on an island. Belize has the largest barrier reef in the entire northern hemisphere and it's just off the coast. Between the barrier reef and the mainland, you have literally hundreds of islands in Belize, and every one of them is encircled with coral. You can imagine what the snorkeling and the scuba diving would be with that environment right at your fingertips.
I've never have been the avid fisherman, but when I go to Belize, I love to go fishing. The variety of fish you catch and the volume of fish you catch in a very short period of time ia great. You don't have time to just sit there and let your rod lay on the water and maybe a fish will bite. It’s more like "Bam!“ There's barracuda, jack, and snapper---both red and yellow, and it's just incredible.
I've gone lobstering and anything to do with kayaking and paddle boarding. Boating I wouldn't do too much because you really have to know your way around because there's a lot of coral under the water and you have to know where you are and what you're doing. So avid boaters they should know that they need to take their time and get to know the place and get to know what the local fisherman know about where to go. Anything to do with the water--- there's manatees, it's just crazy. It's incredible!
There are howler monkeys that are just a short boat ride away. There are islands to visit and hang out in, including several that were built for tourists. There are resort islands that you are welcome to just come and visit, have lunch and beer on the island, and leave if you want.
Sailing is readily available. There are lots of sailboats moored and there are also a couple of international sailing groups like Moorings and Tradewinds that are located right there in Placencia, too.