The main tributaries of the Campaspe River are the Coliban River, McIvor and Pipers creeks upstream of Lake Eppalock and Mount Pleasant, Forest and Axe creeks downstream of Lake Eppalock. Below Lake Eppalock, the major in-stream structure is the Campaspe Weir, which was built to divert water to the Campaspe Irrigation District. It is no longer used for water diversion, but is a barrier to fish migration. Higher flows usually spill over the weir. The Campaspe Siphon, just downstream of Rochester, is part of the Waranga Western Channel, which carries water from the Goulburn system to western Victoria. Water can be released from the Waranga Western Channel into the lower reaches of the Campaspe River, but the siphon is another barrier to fish migration at low-to-moderate flows.
Flows downstream of Lake Eppalock are largely influenced by releases from storage and the operation of the Campaspe Weir and the Campaspe Siphon near Rochester. The Campaspe’s major tributary — the Coliban River — flows through the three Coliban Water storages — the Upper Coliban, Lauriston and Malmsbury reservoirs — before reaching Lake Eppalock. Water for the environment is held and released from Lake Eppalock, with some limited ability to regulate flows further downstream at the Campaspe Weir.
Water for the environment is released from Lake Eppalock to support aquatic plants and animals in and along the river. It can be supplemented by water for the environment delivered via the Waranga Western Channel at the Campaspe Siphon, which provides important flexibility to meeting reach 4 demands. Water for the environment is primarily used to improve the magnitude and variability of flows during the winter and spring. Primary flow measurement points are at Barnadown (reach 2) and downstream of the Campaspe Siphon (reach 4).
Goulburn-Murray Water transfers operational water from Lake Eppalock to customers in the River Murray and to downstream storages (such as Lake Victoria). These inter- valley transfers (IVTs) usually occur in summer/autumn and can significantly increase flows in the Campaspe River at a time when flows would naturally be low. High IVT flows may reduce the amount of suitable habitat for juvenile fish, which rely on protected, shallow areas of water near the edge of the river channel. They can also drown streamside vegetation. Storage managers and the CMA have been working cooperatively to enhance the positive effects and limit any negative effects IVTs may have on native plants and animals. For example, IVTs have been released in a pattern to support native fish migration from the River Murray into reach 4 of the Campaspe River, without affecting delivery to downstream users.