Walden Pond is is not really a pond at all but rather it is a lake located in Concord, Massachusetts.
The lake was created some 12,000-years ago as glaciers retreated once the ice age ran its course. Writer Henry David Thoreau best known for his book "Walden" wrote of his year long stay on the northern shore of the "pond" after his friend & mentor, Ralph Waldo Emerson granted him the use of a cabin. Thus the pond has both a geological history and philosophical one as well.
Swimmers and triathletes have been swimming in the "pond" illegally but that is about to change.
From the Boston Globe:
The goals of the new rules are “managing swimming as a recreational activity at Walden Pond and balancing it with other recreational activities, mainly boating.”
Geigis acknowledged that open-water swimming is already a popular activity at Walden. In an effort to make the pond safer for swimmers and boaters alike, DCR held a series of meetings this summer with swimmers, boaters, and fishermen to draft a set of rules, a set of best practices, and a swimming self-assessment. Public safety officials were also involved in the process, Geigis said, and the Walden Pond Advisory Board approved the draft after it was finished.