By Pat Jenkins The Dispatch "Nutrias have been sighted on Ohop Lake,GÇ¥ a Dispatch reader posted this month on dispatchnews.com. "They have been known to carry diseases and can severely injure small animals and humans if approached. I have personally seen three of these rodents on a dock on the lake and have pictures of them. Please be aware of their presence and keep an eye on your children and pets.GÇ¥ So what is a nutria, and why are they so troublesome? Turns out they have an extensive history in Washington as a desirable critter at one time GÇô and yes, they're not to be trifled with. According to the Washington Department of Fish and Wildlife, nutrias are semi-aquatic rodents native to southern parts of South America. In the 1930s, they were sold throughout North America to fur farmers and, through the critters' natural diet, as a way to control aquatic vegetation. More than 600 nutria farms existed in Washington and elsewhere in the Northwest from the 1930s to the 1950s. Some nutrias escaped into the wild, and others were released when raising and selling them became uneconomical. By the 1940s, nutria were being captured by trappers west and east of the Cascade Mountains. Adult nutrias average 24 inches long from the nose to the base of the tail. The virtually hairless tail itself is another 12 to 16 inches long. Males typically weigh 12 to 20 pounds, while the smaller females are 10 to 18 pounds. When cornered or captured, nutria become aggressive and can injure pets and people through biting and scratching. The color of their fur varies from light, yellowish brown to dark reddish brown -- black, too. They live in lakes, wetlands, sloughs, drainage ditches, and irrigation canals from the Columbia River to Skagit County, and all points in between. As for the health risks from nutrias, Allen Pleus, a Department of Fish and Wildlife (WDFW) unit lead, said they can be infected with tularemia, a bacterial disease that's spread among animals and people by ticks, biting flies and contaminated water. It can be fatal for them. Though not fatal for humans, tularemia can make them sick if they get it from drinking contaminated water, eating undercooked that's infected with it, or cutting themselves while skinning or gutting an infected animal. People infected by tularemia suffer high temperatures, headaches, body aches, nausea and sweats. A mild case may be confused with the flu and ignored. Either way, the symptoms can be easily treated with antibiotics. WDFW "doesn't collect information on the presence of tularemia in nutria,GÇ¥ Pleus said. Some other facts about nutrias: " They are herbivores and eat about 25 percent of their weight daily. In addition to natural vegetation, they eat farm and garden crops and lawns that are near water. " An adult pair can produce two litters per year, averaging five newborns per litter. " Nutrias only live for about three years and prefer living in groups of as many as 13, though adult males sometimes are hermits. They dig burrows in lake banks, with the openings a foot or two underwater. Some have tunnels that are 18 feet long. " Predators of adult nutria include coyotes, domestic dogs, and humans. Great horned owls, foxes, great blue herons, hawks, eagles, and raccoons prey on the young.