papermc/Spigot-Server-Patches/0115-Water-mobs-should-only-spawn-in-the-water.patch

From 3f31cdecde77021afea54370f1fb31ef0621b59f Mon Sep 17 00:00:00 2001
From: Zach Brown <zach.brown@destroystokyo.com>
Date: Thu, 14 Apr 2016 17:48:56 -0500
Subject: [PATCH] Water mobs should only spawn in the water


diff --git a/src/main/java/net/minecraft/server/EntityWaterAnimal.java b/src/main/java/net/minecraft/server/EntityWaterAnimal.java
index f430bdeec..0597edad6 100644
--- a/src/main/java/net/minecraft/server/EntityWaterAnimal.java
+++ b/src/main/java/net/minecraft/server/EntityWaterAnimal.java
@@ -11,7 +11,15 @@ public abstract class EntityWaterAnimal extends EntityInsentient implements IAni
     }
 
     public boolean P() {
-        return true;
+        // Paper start - Don't let water mobs spawn in non-water blocks
+        // Based around EntityAnimal's implementation
+        int i = MathHelper.floor(this.locX);
+        int j = MathHelper.floor(this.getBoundingBox().b); // minY of bounding box
+        int k = MathHelper.floor(this.locZ);
+        Block block = this.world.getType(new BlockPosition(i, j, k)).getBlock();
+
+        return block == Blocks.WATER || block == Blocks.FLOWING_WATER;
+        // Paper end
     }
 
     public boolean canSpawn() {
-- 
2.18.0