A thin or watery milkshake can result from a handful of factors. If the ratio of ice cream to a liquid additive like milk, coconut milk or almond milk is off, your milkshake may come out runny. Likewise, putting crushed ice in your milkshake can lead to a watery consistency as bits of ice melt. If your ice cream to liquid ratio is spot on, you may be blending your milkshake too long. Overmixing can introduce too much heat into the mixture and cause ice cream to start melting.