Navigational hazards are obstacles that can impede the safe passage of ships and other vessels. These hazards can include icebergs (BERG), which are large chunks of ice that can be difficult to spot in the water, reefs (REEF), which are rocky outcroppings that can cause a ship to run aground, FOG (FOG), which can reduce visibility and make it difficult to see potential hazards, and shoals (SHOAL), which are shallow areas of water that can cause a ship to become grounded.