In addition to Wetlands permitting, alterations within the annual high water line at Lake Monomonac or Lake Dennison require a DEP Waterways permit.
As Winchendon doesn't have a local process for Annual Dock/Mooring permitting, this is done directly through MassDEP - via their Chapter 91 process. Their webpage has additional information and guidance for navigating the permitting process and they can be reached via email.
This document from MassDEP speaks to the permitting for Docks through both the wetlands and waterways programs.