Garbage causes damage to local ecosystems, and it is a threat to plant and animal life. Garbage is also a source of food for many animals. A significant amount of garbage is dumped into the oceans.
Most garbage ends up in landfills. These landfills are designed to stop the leaking of material into the rest of the environment to avoid contaminating water supplies. While they are being filled, landfills serve as a popular dining location for birds and other animals, but some of what they eat can cause diseases. Many covered landfills have been converted to parks and recreational areas, but they release methane and other gases through vents as their contents decompose.
Plastic, in particular, has caused a number of environmental issues. Plastic is used for its durability, but this durability also means that it decomposes slowly. It is also strong, so creatures that become trapped in plastic are often unable to break free. Recycling plastic helps to mitigate this harm.
Many countries simply dump garbage out at sea where it diffuses and eventually breaks down. While the long-term impact of this practice is not fully known, there are parts of the ocean where a significant amount of garbage collects and causes harm to plant and animal life in the area.