What is one significant consequence of high mosquito populations?

High mosquito populations are directly associated with a higher incidence of mosquito-borne diseases. When mosquito numbers are elevated, the likelihood of their transmitting viruses and parasites to humans and animals increases significantly. Diseases such as West Nile virus, Zika virus, and malaria can surmount in areas where mosquitoes thrive, posing a serious public health risk. This is particularly concerning in regions where such diseases were previously under control or less common.

The other choices, while they may contain elements of truth in different contexts, do not directly relate to the primary consequence of heightened mosquito populations. Increased outdoor sports activities might occur in certain seasons but does not necessarily correlate with mosquito populations. Similarly, while mosquito presence may affect gardening due to nuisance or bites, it doesn't inherently result in a broad reduction in gardening practices. The growth of the fishing industry is also unrelated to mosquito populations and any direct connection to them is tenuous at best. Therefore, the significant consequence of high mosquito populations is their role in the rise of mosquito-borne diseases, which is a critical area of concern in mosquito control efforts.