First of all, we need to know the conditions for the appearance of monsters in Minecraft:
1 This creature can only be spawned in a sphere located between 24 and 44 blocks close to the player ( the upper limit depends on the simulation distance).
2. The bottom of the creature (the feet of the standing creature, or the entire body if the creature's height is one block or less) can only be generated in air or water blocks. blocks (aquatic creatures). This rule ignores certain natural blocks that do not impede movement, such as grass and flowers.
3. The creature must be spawned on a complete solid surface. (Creatures cannot be spawned on mats, lower half of steps, fences, ascending stairs, redstone repeaters, chests, etc.)
4. This creature cannot be spawned on full transparent blocks, such as glass and. above the leaves.
5. For creatures that can spawn and float in air or water, the block for checking spawn conditions is the air or water block immediately above the first solid block below the spawn position of the creature. (Therefore, ghosts cannot spawn on a carpeted plain, and fish cannot spawn in an ocean that covers the bottom half of the stairs.)
6. Most monsters in the main world cannot be spawned in locations with brightness higher than 7.
7. Most animals in the main world cannot be spawned in places with brightness lower than 7.
To summarize, if the conditions for monster spawning are met in the river, monsters will spawn< /p>