An environmental disaster is a disaster

Disaster

A disaster is a natural or man-made hazard that has come to fruition, resulting in an event of substantial extent causing significant physical damage or destruction, loss of life, or drastic change to the environment...

 to the natural environment

Natural environment

The natural environment encompasses all living and non-living things occurring naturally on Earth or some region thereof. It is an environment that encompasses the interaction of all living species....

 due to human activity. It should not be confused with the separate concept of a natural disaster

Natural disaster

A natural disaster is the effect of a natural hazard . It leads to financial, environmental or human losses...

.
In this case, the impact of humans' alteration of the ecosystem

Ecosystem

An ecosystem is a biological environment consisting of all the organisms living in a particular area, as well as all the nonliving , physical components of the environment with which the organisms interact, such as air, soil, water and sunlight....

 has led to widespread and/or long-lasting consequences. It can include the deaths of animals (including humans) and plants, or severe disruption of human life, possibly requiring migration.
Environmental disasters can have an effect on agriculture, biodiversity, the economy and human health.