During an experiment investigating the efficacy of washing oiled birds with saltwater compared to freshwater, eight out of forty-four mallards (Anas platyrhynchos) became ill within 2-9 hours after the washing process. They presented with weakness and inability to stand. A presumptive diagnosis of capture myopathy and heat stress was made based on clinical signs and a history of prolonged periods of stress during catch up and high ambient temperature (34°C). All affected birds had been washed and rinsed in seawater (~3.5% saline). Treatment for capture myopathy was started immediately and involved aggressive fluid therapy with intravenous and oral isotonic fluids as well as meloxicam and midazolam. Despite treatment, five of the sick birds died after several hours. Initial findings on gross necropsy of the five dead birds revealed pale thigh muscles, consistent with myopathy, as well as brain congestion and cardiac haemorrhages. Blood samples were taken from the remaining live birds and revealed elevated serum sodium and creatinine kinase levels. The treatment protocol was immediately changed as the treatment for hypernatremia is the opposite for capture myopathy because serum sodium levels need to be reduced slowly to prevent swelling of the brain. Drinking water was restricted, with freshwater being offered to the birds at a rate of 0.5% of body weight every 30-60 mins throughout the day until they had drunk a total of 100-120 ml (twice their normal fluid maintenance needs). As the birds’ clinical signs improved they were slowly offered increasing amounts of freshwater every 30-60 mins and after 4 days of treatment all three birds had recovered. Changes made to the husbandry procedures on Day 2-4 of the experiment to prevent further illness will be discussed. The mallards used in this experiment were raised in captivity and freshwater-adapted and therefore appeared highly sensitive to saline water.