The fiercest impact that the amphibians endured in the recent decade is diseases. The mass mortality of European Common Frogs in several areas in southern England in 1990s is caused by viral infection. Of the most noteworthy is the global outbreak of chytridiomycosis. This is caused by the chytrid Batrachochytrium dendrobatidis, a single-celled fungus that invades the skin of the amphibians. The infection almost led to the catastrophic collapse of amphibian populations in parts of Central America, eastern Australia , and the western United States . Chytridiomycosis are found in almost every continent of the world, but were first found in captive animals. It is unclear if this is an ineradicable new strain, or the amphibians have become more sensitive to the diseases that they were able to coexist in the past due to various elements.

It is inevitable to consider single factor when focusing the investigations on the causes of possible decline in amphibians; in reality, the amphibians may be threatened by different causes simultaneously. Some studies have already considered the interaction between two or more factors, and have proven the significant synergistic effect among the factors. For example, the climate changes in the western United States , the increased ultraviolet B radiation, and synergistic effect of the diseases have already induced the decline in the numbers of amphibians. Climate changes have reduced the water level of spawning pool. The consequence made it harder for the eggs to be protected by deeper waters against ultraviolet light; further, the eggs become more sensitive to Saprolegnia, a type of fungus that can induce disease. Saprolegnia can invade and kill amphibian eggs.

Most amphibian eggs and larvae lack defensive capabilities against predators such as fish; in addition, amphibians are being harmed by the fish released into the ponds, lakes, and streams by humans. For instance, the mosquito fish being released everywhere in the world to control malaria-causing mosquitoes, and trout being introduced for entertainment. The two species of fish have found that amphibian larvae are easily caught and attracted prey. The major cause for the loss of several species of amphibians in the Californian lakes in the mountain region is due to the introduction of trout that became predators.

Fish are not the only enemy introduced; amphibians may threaten local species if they are relocated to places where they do not belong. The American Bullfrog (Rana catesbeiana) is an example. They were introduced to various parts of the world in order to maintain frog leg trading; however, its larvae would grow relatively large and would win in the competition against the larvae of local species.