As with most all of the island, the water is very shallow and has sea grass. The beach itself is soft white sand. The reef is 1/3 mile of shore and you can take our kayaks out there to snorkel - there is a mooring right at the reef across from La Perla.
I just stayed at La Perla - unfortunately the whole island (and a lot of other Caribbean islands?) is having an issue with loads of seaweed washing ashore as well as clogging up the waters at the shoreline. Some fellow travelers staying at a resort farther south had commented that they had tried to swim off the shore but due to the shallow waters, slimy sea grass on the sandy bottom, and the boat traffic, it wasn't very good. There is a really nice beach/swimming area on the west side of the island accessible via golf cart and about a 15 minute drive from La Perla. If you are looking for shore access to swimming, that would be my recommendation. Otherwise the snorkel trips available with various companies are amazing. I didn't try kayaking and snorkeling myself from La Perla - you would have to cross the boat "highway" which can have a fair bit of traffic but would be doable. Hope this helps! It's a beautiful place to visit!
Get an answer from La Perla Del Caribe staff and past guests.