In 1888, the Roxburgh Amalgamated Mining Co. constructed an 18ft high rock dam on the Upper Teviot River, flooding an area called ‘Dismal Swamp’. The resulting lake was named after a governor of New Zealand, William Hillier, Fourth Earl of Onslow. Originally built as a water supply for gold mining and irrigation purposes, in 1924, the dam starting operating as an irrigation-power scheme. Between 1888 and 1938 the dam was raised three times. A new dam was built just downstream of the original structure in 1982 and this increased the area of the lake from 367ha to about 830ha. Lake Onslow carries a large population of brown trout averaging around 1-1.5kg, although fish of over 3kg are not uncommon. The fish population is self-sustaining due to excellent spawning habitat in the lake’s major tributaries. Set in high tussock grasslands, Lake Onslow is a great place to fish if you love the wide-open spaces and natural beauty of Central Otago.
Lake Onslow is situated about 22km east of Roxburgh, at the northwest end of the Lammerlaw Range. There are three main access routes to this water. The two most popular are from Millers Flat and Roxburgh East. If you are travelling from Dunedin, turn right at the Millers Flat Hotel and cross the bridge over the Clutha River then turn left and carry on until you come to Timaburn Road. The lake is signposted from here. When travelling from Roxburgh the quickest way is to cross the bridge over the Clutha in the middle of town then turn right. About 1km along turn left up Wright Road, then left onto Sander’s Road and finally left again onto Lake Onslow Road. The other access is from the southwestern end of the Styx basin on the Upper Taieri River, this is the other end of Lake Onslow Road and is unmetalled, therefore only suitable in dry conditions.
There is good access to the lake edge in several places. A boat ramp is also present near the main huts. A boat is an advantage of you really want to explore Lake Onslow but it is not essential to angling success. Most of the access route are private roads made available for public use by permission of the landowner. Make sure you take your rubbish with you when you leave.
All methods can be used. Trolling and spin fishing appear to give the best results, but worm and flyfishing are also both popular and successful. Due to excellent spawning grounds the lake is kept very well stocked.
From September through to the end of May, spin anglers have most success with fishing along the shallow margins. In June, July and August the shallow edges often freeze over, therefore fish will head for the deeper water. Toby’s, in either ‘black and gold’ or ‘banana’ colours, or size No 3 green and gold Veltic spinners are most popular. In the warmer months, it can be better to use smaller lures such as Black Wedges and Tylo’s. Rapalas and Tassies Devils can also be very effective, try the colours suggested in the trolling section.
Trolling can give some excellent results, especially if there is a slight breeze rippling the water surface. When the sky is dark, use light coloured lures, especially silver or gold, when it is bright and sunny darker shades are more effective. It is common to fish a feathered lure 50cm in front of your main lure on this water. Those mentioned in the fly section are best. As well as the lore mentioned in the spinning section, Rapalas in rainbow trout, brown trout or perch colours work well as do Tassie devils in traffic light or frog patterns. Most trolling is done with ordinary nylon spinning lines and about 100m of line out. Remember, when trolling you have the option of fishing anywhere on the lake, so be courteous to anglers fishing from the shore and give them plenty of room.
There are two methods of bait angling. The traditional method is using a sinker, but because of the shallow and often weedy nature of the lake, suspending your bait (about a metre) beneath a float is sometimes more practical. The latter method is used by fishing with the wind behind you. If using the traditional method, fish close to the shore as trout are often feeding in about 1.5m of the water. Please do not dig for worms around the lake edges.
Fly anglers start the season using dark coloured feathered lures on a floating or sink tip line depending on the depth of water. Woolly Bugger, Hammill’s Killer, Monsum’s Bully and Mrs Simpson are proven patterns. Dry flies to use in spring and early summer are Royal Wulff, Cochybondhu and any other brown or green beetle imitations. In January and February Cicadas come on, then later in the season Black Gnats and Peveils of the peak are used to imitate the adult diving beetles. Throughout the season, dawn and dusk fishing can be superb due to incredible midge hatches, Midge pupae and emergers in a range of colours should be carried, as well as some Adams dries to imitate the adult midges. Damselfly and water-boatman nymphs are also an essential part of the fly anglers armoury.