Take for instance the conditions of the tropical Pacific surface temperature during the strong 2015/2016 El Niño in Fig. 1a, which is one of the strongest on record. Temperatures rose above 2 degrees Celsius in the central and eastern Pacific and it was so strong it caused severe bleaching of the corals in the Great Barrier Reef. One of the most easily recognizable effects of El Niño is the decrease in the marine wildlife and the fishing industry, so much it became the reason behind its name -- Peruvian fishermen ironically nicknamed the anomalous warming of the Peruvian Current waters after the Boy Jesus because they couldn't catch much fish as usual around Christmastime. 
La Niña follows as an obvious companion, named to describe the anomalously cold waters in contrast to El Niño. The 2010/2011 La Niña in Fig. 1b was also one of the strongest on record and it caused several extreme floods throughout the world, from Australia to the Amazon Basin. These adverse effects such as droughts and floods caused by a particular phenomenon, like ENSO, on a remote locality away from its center of activity is called a Teleconnection by the climate scientists and that is the main reason why it's so important to monitor and study the causes of ENSO activity.
But how can these ENSO events be important for the Amazon Basin? First, this is the largest drainage basin in the world and is home to both an immense rainforest and even greater biodiversity. It has a pivotal role in the stability of the global climate system by absorbing carbon dioxide from the atmosphere and driving the hydrological cycle in other continental basins through its contribution to large-scale atmospheric moisture transport.