The mapped river is about eighty-five kilometres of mainstem, and it earns that length slowly. Like the other rivers on this side of the range it begins as creeks draining tussock marshland, fed from the snow on the Brindabellas, and early in the season a large volume of cold water comes down those drainages at once. The river twists north through Namadgi National Park and the Lower Cotter Catchment before it reaches the Murrumbidgee.

Three dams sit on it. From the top: Corin, then Bendora, then Cotter Dam near the bottom. The territory’s rules name those dams as the boundaries of what may be fished, and they also shape the river’s behaviour, because the trout water sits below one storage and above another. Eighteen gauges across the river and its catchment supply current readings when available. The river’s year and flow-duration chart use the Cotter River below Bendora Dam record; the fall of the river and the bank survey cover the whole mainstem. Each stretch has its own page, and the river map draws the four of them with the three reservoirs as the stops between. The character: a cold, clear stream of runs, bends and pools, big enough to need a proper nymph rig in spring and readable enough to sight-fish by summer.

Rainbow trout carry the strongest record on the Cotter. Brown trout appear in the authority’s trout-water listing and in one low-confidence observation joined to the whole river. Neither tells you that a particular pool in the Bendora-to-Condor reach holds one, so treat rainbows as the main expectation and a brown as possible.

The food is what you would expect of a cold clear river with grazing and pine country along it. Mayfly duns come off on warm afternoons, even early in the season. In the plantation country the ant falls are the event of the summer, the kind of day the river’s regulars plan around. Where the banks run to tussock a hopper works from midsummer.

The Cotter catchment also matters to fish you must not touch. Macquarie perch, trout cod, silver perch and two-spined blackfish are among the seven species the ACT lists as totally protected. If you catch one, release it with as little injury as you can and report it to Access Canberra.

The season opens on the October Labour Day long weekend and runs to the end of the June King’s Birthday long weekend; those dates move with the calendar, so check the current brochure. Within that window the river has three moods.

Spring is the melt. The river can be heavy and freezing at the opening, and the fishing is deep nymphs in the slower water off the main current, with an afternoon dun hatch as the reward if the sun comes through. Summer is the dry-fly season: lower, clearer water, sighted fish on the big bends, ants out of the pines and hoppers on the tussock banks. Autumn is deliberate fish in low water until the season closes after the June long weekend.

Two rigs cover the river. In heavy water, a deep nymph rig under an indicator, fished in the slower, less turbulent runs beside the current so the flies get down. Work the runs one at a time and expect the take at the tail-out as the drift straightens. In clear water, a single dry or a dry-dropper, and before you cast, a look. Find a high vantage point above a deep bend and watch the mottled shapes that were rocks a moment ago turn into fish. Take your time in those places and hunt one fish rather than covering the pool.

The ACT rule on gear is worth knowing before you rig up: in trout water the rod may carry no more than two flies, or one lure, and you may fish only one rod at a time.

The trout water runs through Namadgi National Park and the Lower Cotter Catchment Reserve, and the territory’s parks service lists Cotter Campground, Cotter Bend, Cotter Avenue and Casuarina Sands among the recreation sites on the lower river. For the trout water, use formed public roads and tracks, obey signs, and check the ACT Parks nature park finder before you go. A line on a map is not permission to walk it.

The water above Bendora and above Cotter Dam is closed to fishing at all times. It is a drinking water catchment, and the closure is absolute.

Early-season flows are the safety point. Snowmelt can have the river sweeping debris past, and a fish hooked in that current will use it. Wade with care, or do not wade, and come back in a month if the river is high.

The ACT publishes its rules in an annual recreational fishing brochure and on the territory’s fishing pages, and no licence is required to fish the territory’s public waters. Three classifications touch this river.

The Cotter between Bendora Dam and the Condor Creek junction is Trout Water. In trout water, fishing is open from the start of the October Labour Day long weekend to the end of the June King’s Birthday long weekend; only artificial fly and lure fishing is allowed in the open season; bait fishing is prohibited; you may use one rod at a time and a landing net; the rod may carry no more than two flies or one artificial lure; and it is an offence to possess a handline, more than two rods, a rod rigged for bait, or any net other than a landing net in or beside the water.

The Cotter above Cotter Dam wall to the junction of Condor Creek, including the Cotter Reservoir, and the Cotter and its catchment above Bendora Dam wall, including Bendora and Corin reservoirs, are Prohibited Waters. Fishing there is not allowed at any time.

The Cotter below Cotter Dam is Open Water, with the more permissive open-water gear rules.

The ACT sets a minimum size and a combined bag limit for trout across its trout and open waters. This page does not state the numbers; take them from the current territory brochure before you fish. Penalties apply under the Fisheries Act 2000, and illegal fishing can be reported to Access Canberra.