Unfortunately, there seems to be some confusion or error in the question provided. Janesville Traxler Park, where Rock River Beach - Lagoon boat ramp is located, is actually in Wisconsin, not Tennessee. Additionally, there is no body of water in Janesville Traxler Park called "Rock River Beach - Lagoon."

However, to provide some general information about boat ramps, they are typically constructed to allow boats to be launched or retrieved from a body of water. The width and design of a boat ramp can vary depending on the size and type of boats it is intended for. The body of water a boat ramp services can also vary, from a lake or river to the ocean. The types of watercraft allowed on the water can also vary depending on local regulations and restrictions.

In order to provide more accurate and specific information about a boat ramp, it would be necessary to research the particular location in question.