The Donnelly River has a length of 150km. The upper part of the river flows through cleared farmland but most of the catchment is still forested and the river is fresh. The river is stocked each year with rainbow trout (yearlings, fry) and brown trout (yearlings). Several of the major tributaries are also stocked with rainbow fry, including Carey and Manjimup Brooks. Redfin perch are present but are not common and if caught must not be returned to the river. Redfin can be taken by a variety of methods including spinning with hard body lures, jigging soft plastics in among the snags or bait fishing with worms. Trout can be caught from up near the SW highway bridge all the way down to the mouth of the river for most of the year, but in the summer months the upper reaches usually dry to a series of shallow pools where water temperatures are too high for trout.
The most popular fishing method for trout is spinning using small hard body lures, and most spin fishers target the longer runs and deep pools. There are many logs and branches lying in this river. To avoid snags remove the middle treble, and use only a single hook at the tail of the lure. This will also help prevent damage to undersized fish. Bait fishers target the deeper pools where the current is slower using worms and sweetcorn. Fly fishers often target faster runs and the base of falls and rapids. Popular flies include various minnow patterns swung across and downstream in fast water and prospecting pocket water with a variety of nymphs such as gold bead flashbacks. During summer dry fly fishing can be productive using hopper and caddis patterns. Redfin can be taken by a variety of methods including spinning with hard body lures, jigging soft plastics in among the snags or bait fishing with worms. There are many access points where road bridges cross the river and from a maze of forestry roads. The Bibbulmun Track follows the river for more than 30km west then south from Donnelly River Village. Best times to fish are in late autumn when water temperatures fall and river levels rise and in late spring when water levels start to fall. The mouths of brooks and below rapids are hotspots at these times.