The Tummil River is a small river in south Marlborough flowing from its source at Lake Alexander into the Avon River which in turn is a tributary of the Waihopai River.
For much of its length, the Tummil flows through the Ferny Gair Conservation Area, with significant amounts of manuka and beech forest.The area is extremely rugged with the river tracing a narrow path through steep, rocky country, with a number of small waterfalls, and with large boulders in stream bed. The lower reaches of the river are more open, and pass through farm land.
A tramping route follows the river to Lake Alexander, frequently crossing the river. Access is via private property and requires payment of a fee.