This is an area literally oozing with Tasmanian colonial history as the search for fresh water drew the early European explorers.
A well maintained track beside the river will lead you to the cache, which can be located after a short scramble up the bank. It's not too difficult to get to or locate.
As an optional extra... a short walk beyond the cache will bring you to the ruins of the Supply River Mill and Tasmania's earliest colonial graffiti.
In 1804 the Lady Nelson sailed up the Tamar River to discover the Supply River. The expedition's mineralogist: Adolarius Humphrey carved his initials deep into the rock. The legend 'AH 1804' is still legible some 220(+) years later.
The graffiti coordinates are listed below and will involve some rock hopping in the river bed.