Natural environments, namely green and blue spaces, have been found to have positive influences on mental health outcomes globally. As the contribution of poor mental health to the disease burden increases, the mechanisms through which natural environments may improve health are of growing importance. This study creates a novel visibility index methodology and investigates whether i) views of natural environments and ii) access to natural environments, are associated with psychological stress and physical activity in Wellington, New Zealand. It also builds upon the work conducted in New Zealand as the first study to investigate links between blue space and mental health and provides an insight into the mechanisms through which increased natural environments may improve health. Individual level data for 442 individuals from the New Zealand Health Survey was obtained and Geographical Information Systems (GIS) were used to investigate whether area-level exposure to natural environments influenced their psychological stress and levels of physical activity. Results from regression analysis indicate that increased distant visible green space (beyond 3km), visible blue space, and a combination of green and blue spaces from neighbourhood centroids reduce psychological stress. Some access measures to natural environments were found to have positive associations with psychological stress, however increased proximal access to green space was associated with decreased physical activity. The findings conclude that the visibility of natural environments appears to have stronger associations with stress reduction than access to them. The findings of this paper should influence urban development and inform decision and policy making, particularly the development and/or relocation of health related facilities.