The Berks, Bucks & Oxon Wildlife Trust (BBOWT) is hoping to extend its protection of meadowland at Chimney which is midway between Newbridge and Tadpole Bridges.
The Trust wishes to buy the Duxford floodplain opposite Chimney and on the south side of the Shifford Lock Cut.
The land is downstream of Tenfoot Bridge with the Old Thames as its eastern boundary.
In the early days, the Thames Path followed the Old Thames to the ford at Duxford before passing through Duxford Farm and rejoining the towpath at Tenfoot Bridge.
In the 1980s the towpath alongside Chimney meadows was overgrown and rarely used.
BBOWT has launched an appeal for £220,000 to be raised by 30 September to purchase the 113 acres which at present is unprotected.