Where do hydras spawn?

Could you please clarify for me the exact locations where hydras are known to spawn? Are there any specific biomes or environmental conditions that they tend to favor? I'm particularly interested in understanding if there are any patterns or commonalities among the places where hydras have been encountered in the past. Additionally, are there any precautions or strategies that one should consider when exploring these areas in search of hydras? I'm eager to learn more about this fascinating creature and how to best approach it.