As I have explained in past posts, there are a number of affects that rainfall has, especially in relation to the increase in available food.
In the US it is common for rain to flood many grubs and worms from their holes along the muddy banks of the water, making them an easy meal for hungry fish. Here in Argentine, I have learned that this principle is very applicable. Along the banks of the lagoon there is a type of large worm that burrows in the muddy banks close to the waters edge. This “worm” seems to be more of an eel, yet scaled, with no eyes; just a large mouth. They range in length from very small to up to about 8 inches. The recent rain has brought the worms out of their holes, making the lagoon once again sustainable for fish.
I met one fisherman in town who was fishing with his son. The night before they had caught a number of these worms, and were now using them as bait, resulting in a beautiful catch of 17 impressive catfish. I have found that when fishing in such conditions, the best pattern to use is a velvet eel, or a large woolly bugger, both of which mimic a similar worm that is sure to bear results. When fishing in rivers in the northern US that are under the same conditions, it is best to stick with a woolly bugger, fishing it along the edge of the banks where tree-roots overhang the water. Along such areas trout will lay under the covering and feed of whatever finds its way into the water below.