The populations of hyacinth macaws ( Anodorhynchus hyacinthinus), an emblematic species, have suffered declines due to many environmental factors. The Hyacinth Macaw Institute’s actions are showing positive outcomes for the conservation of A. hyacinthinus. However, environmental issues, such as fires and deforestation due to inefficient and unsustainable cattle ranching practices, are a threat to the biodiversity. Another major threat is the reckless use of pesticides. The objective of this manuscript is to describe the findings, in the Pantanal, of three dead hyacinth macaws and to investigate their cause of death and conservation implications. A necropsy was conducted on two individuals and biological samples were collected and sent to conduct toxicological exams to test for organophosphates, organochlorines, and carbomates. Compatible with other findings, results showed a highly dangerous level of organophosphate, 158.44 ppb. We describe for the first time, a rare, isolated but unusual mortality event associated with organophosphate pesticide poisoning of hyacinth macaws. Mortality reports for bees and other bird species on how the improper use of pesticides can potentially cause the contamination of food and water resources are discussed. These factors are antagonistic to long-term efforts to preserve wildlife and carry out other conservation efforts in Brazil’s southern Pantanal.