GreenYour.com wrote:

You do not need to purchase chemical bug sprays. Using products containing the insect repellent DEET may be harmful to fish and other aquatic wildlife, as well as human health.

One of the most widely used ingredients in store-bought conventional bug sprays for personal use is N,N-Diethyl-m-toluamide, or DEET, as it's commonly known. DEET, which is designed to repel, rather than kill, insects. DEET is used by an estimated one-third of the US population each year. Although DEET is approved by the US Environmental Protection Agency (EPA), it is a known eye irritant and can cause rashes, soreness, or blistering when applied to the skin. Additionally, DEET has been linked to neurological problems; according to the EPA, at least 18 different cases of children suffering adverse nuerological effects, as well as the deaths of two adults, have been associated with DEET. Researchers at Duke University Medical Center have found that DEET causes diffuse brain cell death and behavioral changes in rats.[1]

DEET has been shown to have a negative impact on wildlife and water sources in production and during use. DEET is toxic to birds and aquatic life. DEET has been found in approximately 75 percent of U.S. water sources, including the Mississippi River.[2]

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1) Cornell - DEET Mosquito Repellent: New pharmacology study of impacts
2) About.com - The Downside of DEET Insect Repellents: Health and Environmental Risks Associated with the Use of DEET