That is correct! (It started as a dumb, vague reference to Sword in the Stone, funny enough.) There are many theories that the the Bermuda Triangle is actually a series of wormholes that disappear ships to other worlds, a hole in the planet's electromagnetic forces that messes with communications and navigation, and a number of other things. For our fictional setting of Avalon, we're saying that one of those wormholes leads to the lake, which at times can result in the arrival of both functional and wrecked ships, as well as mixes some areas of the lake with salt water using magic to protect creatures' health, which is why sometimes non-fresh water creatures will show up.

The docks themselves don't have ships available for Camelot's citizens to travel for the most part as Avalon is ultimately a fae realm and is under the jurisdiction of the Queen of Elphame, and after the separation of the north and south and Celliwig's shut down long ago, only fae kind and incidental arrivals (such as the pirates described in Salacious Sailors quest, who eventually get sent back to where they came from by the Lady of the Lake) are permitted to use ships in the waters. Camelot's residents do not have permission to sail the waters, which is why the offering of aquatic mounts was such a big gesture! (And why Merlin didn't just have everyone raise ships and hop aboard instead of sending an offering with the Traders.)

So yes, there are more things in the waters-- some that will be revealed in the future, and others that a chat with the Lady of the Lake might lead to. (She likes gifts of food and dresses, if you want her in a chatty mood.)