I must admit that I don't do too much fishing on really flooded rivers. Floods generally result from heavy rain, and heavy rain generally arrives on southerly or westerly depressions, bringing low pressure, wind and warmer air. This is conducive to good stillwater fishing; my preference is to go after big carp, but pike and roach can also feed well on warm, windy days - especially on gravel pits.
However, sometimes the river calls, so what's to be done? Firstly, pick a stretch you're familiar with. Not only is it difficult to assess likely spots when faced with an unfamiliar river in a brown flood, it can also be downright dangerous - especially if the water's over the banks; it's all too easy to put a foot into a ditch you didn't know was there, or go off the bank into a cattle drink. If you've fished the stretch before - or at the very least walked it a few times at low water - you will know the location of fallen trees, submerged bulrush beds, weedbeds and other obstacles, and be able to avoid them.
Fish need two things; safety and food. Under normal conditions, safety is usually provided by cover of some sort; weedbeds, overhanging trees, undercut banks and so on. Food is sometimes available nearby, but often it is not, so they have to go searching for it. A flooded river, especially if it is highly coloured, allows them to move into areas that are normally too shallow or exposed. That shallow run on the inside of the bend where you stood last summer to trot along the far bank treeline might now be five feet deep and holding a huge shoal of roach.
Floodwater also changes the position of things. Obstructions to carefully presented baits that grow up from the bottom, or hang down from above, can be swept horizontal in the increased flow. The tantalising swim by the willow where you found it impossible to roll a legered bait beneath the trailing branches, might now be clear. The extra current will have scoured the river bed and the branches still provide cover for a shoal of chub, even if they are only trailing in the upper layers. For the same reason, when fishing upstream of your position, you must remember to cast slightly further downstream of reedbeds, trailing branches and so on.
Just about the worst places to try are the ones the books show, usually with an illustration of arrows circling around a convenient crescent in an otherwise straight bank. Eddies, backwaters and slacks are the dumping ground for all manner of debris washed into the river. Not only that, but the extra height of water usually corresponds with an increase in width, unless the river is set into a channel with vertical sides. This means the margins at low water are now several feet - maybe even yards - further out. Between them and where you sit will be the sloping bank, which back in the summer was covered in head high nettles, brambles, hogweed and balsam. Do you really want to be dropping a bait into all that? Even if a fish found it, you'd struggle to fetch it out again, and when you reel in at the end of another blank afternoon you'll probably get hung up and lose your hook, lead and everything else.
No, forget the river margins. Forget too the deepest holes where the fish go in summer to escape the heat of the day; these sudden depressions in the river bed also catch rubbish coming down, which drives the fish out in search of more congenial surroundings. Look for somewhere with a steady flow over a clean bottom, and don't worry too much if it's a bit quick, or usually too shallow to hold anything but minnows. Even big fish will lie quite happily in a foot of water if it's coloured enough. Just remember to keep off the skyline; you might not be able to see the bottom through the sediment, but be sure the fish will know you're there. Visibility through a brown flood might only be 50% of what it is in clear water, but you'll still block out the same percentage of whatever light is penetrating if you stand up against the sky.
