do you have a big enough pond? and are you sure you're on the right biome for the quest fish?
Could be that not every pond is big enough. I thought fishing power was the really determining factor (I almost always fish with 125 power or more). I thought about the biomes issue but it was never a problem for the longest time. If I'm in a snow biome that was taken over by hallow does that not count as snow anymore? That could be the only noticeable change, that I have few "pure" biomes right now in my main world.
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