The Mast Pond was constructed by Dutch prisoners of war who were paid one-and-a-half pennies a day, although following complaints by unemployed townspeople the Dutch were dispatched to Portchester Castle and local labour hired in their place. 

The Pond is linked to Portsmouth Harbour by a tunnel which runs from its western end underneath Main Road and Boathouse 4.  It was used to store timbers to prevent them from seasoning unevenly or cracking before they were made into masts.  Tidal flow was partly controlled by a drop-gate at the western end of the tunnel.

The new hydraulic lock gates installed by the Trust in 2000 now maintain a minimum level of water in the Mast Pond and prevent Boathouse 6 flooding at spring tides.