--- a/net/minecraft/world/entity/animal/EntityDolphin.java
+++ b/net/minecraft/world/entity/animal/EntityDolphin.java
@@ -63,6 +63,12 @@
 
 public class EntityDolphin extends EntityWaterAnimal {
 
+    // CraftBukkit start - SPIGOT-6907: re-implement LivingEntity#setMaximumAir()
+    @Override
+    public int getDefaultMaxAirSupply() {
+        return TOTAL_AIR_SUPPLY;
+    }
+    // CraftBukkit end
     private static final DataWatcherObject<BlockPosition> TREASURE_POS = DataWatcher.defineId(EntityDolphin.class, DataWatcherRegistry.BLOCK_POS);
     private static final DataWatcherObject<Boolean> GOT_FISH = DataWatcher.defineId(EntityDolphin.class, DataWatcherRegistry.BOOLEAN);
     private static final DataWatcherObject<Integer> MOISTNESS_LEVEL = DataWatcher.defineId(EntityDolphin.class, DataWatcherRegistry.INT);
@@ -190,7 +196,7 @@
 
     @Override
     public int getMaxAirSupply() {
-        return 4800;
+        return maxAirTicks; // CraftBukkit - SPIGOT-6907: re-implement LivingEntity#setMaximumAir()
     }
 
     @Override
@@ -231,6 +237,12 @@
             ItemStack itemstack = entityitem.getItem();
 
             if (this.canHoldItem(itemstack)) {
+                // CraftBukkit start - call EntityPickupItemEvent
+                if (org.bukkit.craftbukkit.event.CraftEventFactory.callEntityPickupItemEvent(this, entityitem, 0, false).isCancelled()) {
+                    return;
+                }
+                itemstack = entityitem.getItem(); // update ItemStack from event
+                // CraftBukkit end
                 this.onItemPickup(entityitem);
                 this.setItemSlot(EnumItemSlot.MAINHAND, itemstack);
                 this.setGuaranteedDrop(EnumItemSlot.MAINHAND);
@@ -389,7 +401,7 @@
 
         @Override
         public boolean canUse() {
-            return this.dolphin.gotFish() && this.dolphin.getAirSupply() >= 100;
+            return this.dolphin.gotFish() && this.dolphin.getAirSupply() >= 100 && this.dolphin.level.getWorld().canGenerateStructures(); // MC-151364, SPIGOT-5494: hangs if generate-structures=false
         }
 
         @Override
@@ -489,7 +501,7 @@
 
         @Override
         public void start() {
-            this.player.addEffect(new MobEffect(MobEffects.DOLPHINS_GRACE, 100), this.dolphin);
+            this.player.addEffect(new MobEffect(MobEffects.DOLPHINS_GRACE, 100), this.dolphin, org.bukkit.event.entity.EntityPotionEffectEvent.Cause.DOLPHIN); // CraftBukkit
         }
 
         @Override
@@ -508,7 +520,7 @@
             }
 
             if (this.player.isSwimming() && this.player.level.random.nextInt(6) == 0) {
-                this.player.addEffect(new MobEffect(MobEffects.DOLPHINS_GRACE, 100), this.dolphin);
+                this.player.addEffect(new MobEffect(MobEffects.DOLPHINS_GRACE, 100), this.dolphin, org.bukkit.event.entity.EntityPotionEffectEvent.Cause.DOLPHIN); // CraftBukkit
             }
 
         }