The Turtle Shell's Water Breathing effect immediately begins counting down from 10 seconds as soon as the player's feet touch the water, when it should begin as soon as the player's head is submerged below the water's surface.

Also, if you equip the Turtle Shell while standing in water, it will not give you the Water Breathing effect until you leave the water. This makes it difficult to reset the effect's timer when emerging from underneath the water for air. The timer should reset as soon as the player's head is above water, similar to how resetting the breath meter works.