Why are trout harder to catch during hot weather?
Trout are cold water fish and don't like it when the water temperature gets too warm. They need lots of oxygen and the amount of oxygen water holds decreases the warmer it gets.
When the water temperature goes over about 22°C the oxygen level drops so much that trout get uncomfortable and they'll typically stop feeding until the water cools down again.
How does warm water affect trout behaviour?
The water in lakes isn't usually a constant temperature. The surface gets warm, but the depths and any shady spots often remain cooler, so trout will drop to the bottom or seek shade to escape the heat.
In many lakes the water can become stratified and there are layers of warm and cool water. The warm water sits on top of the cool water lower down and the trout will lie in the water that's cooler.
That layer can move if it's windy, or if there's a current in the water, so the fish don't always show where you might expect them. Strong winds can mix the layers up and push the warm layer to one end, so moving around can sometimes put you in areas where the fish have moved to keep cool.
Do trout stop feeding when it's too hot?
If it's too warm they'll stop feeding during the day, but they will become active again when it's cooler in the early morning and late evening, so these are the best times to fish. You can still catch them during the heat of the day, but it will be much, much harder.
Where should I target fish during hot weather?
Find the deepest, coldest water, as the trout will most likely have gone there to escape the heat. They'll continue to feed readily in these spots, providing the temperature isn't too high. Shady areas can also hold more fish.
The dam walls of reservoirs often hold deep water and the trout can bunch up there when it's warm, so that's the first place to look. Also try any parts of the lake where the sides are steep, as the steep sides typically extend below the surface into deeper, cooler water below.
Since oxygen gets depleted in hot weather, trout are also drawn to areas where there's water movement or aeration. Some small still water fisheries turn on their aerators during warm weather to keep the fish happy, and you'll often find the fish (especially bigger ones) drawn to the bubbles.
Natural springs and inlets bringing in cooler, oxygenated water will also attract the fish. If you're fishing a small still water trout fishery it's worth asking the locals or the fishery owner where the spring inlets are, as this knowledge could help you locate the areas into which the trout have moved.
When is the best time to fish for trout?
Getting to the lake early will let you target trout that have moved into the shallows or towards the surface after the water has cooled overnight. However, staying late is usually most productive, especially as this often coincides with the hatching of insects, upon which the hungry trout will often gorge themselves.
Do I need to do anything different when catch and release fishing in hot weather?
Yes, you need to look after the fish with greater care when the water is warm. Ideally, you shouldn't fish for trout in water that is too warm as they can suffer oxygen stress and have difficulty recovering, but it's fine if you're covering them in deeper, better oxygenated waters.
Firstly, don't remove the fish from the water if you're fishing catch and release. Instead, unhook them in the water, ideally without touching them, using forceps or a Ketchum release tool, or net them and unhook them in the net.
Lifting them out of the water and exposing them to hot sun won't do them any good, so avoid this at all costs so your catch goes back unharmed. When you're returning them, give them plenty of time to recover so they swim off to fight another day.
What line should I use?
That depends on the conditions and the water. In deeper lakes you'll often find that the hot weather puts the fish down deep, so a sinking line could put you into the zone in which the fish are lying. However, in other waters, the fish might still be near the top so a floating line or intermediate might be fine.
What flies work best in hot weather?
In very hot weather, trout will often stop chasing flies so readily. Fishing a pattern static, either under an indicator or by fishing a buoyant fly on a sinking line, can help attract fish. Their lethargic behaviour means they're more likely to take a fly that's not moving much, or at all. Slow down your retrieve or keep the flies completely static.
A wide range of patterns will work, but blobs, buzzers and other patterns that can be suspended beneath indicators or straight-lined will do the trick. FABs and boobies work well on reservoirs when used on a sinking line.