How long do they live?   5 years, 10 years, 20 years?   I saw one in a local community pond that looked to be 3 to 4 feet in length.  

Grass Carp live 10-12 years on average. I have heard reports of them living 15-18 years. The only kind legal to stock in Texas are Triploid (Sterile).

However, the useful life of a grass carp is 5 to 7 years. During those first 5-7 years a grass carp can eat up to 3 times its body weight in vegetation. After 5-7 years, their appetite diminishes with each passing year they eat less and less, although they root around the bottom, causing some lakes to become turbid (muddy). We have electro fished them up to 45 lbs.

We generally like lakes that have them, but like anything too many is a huge problem. When used correctly, they are great in lakes that have a vegetation issue. The key is stocking the right amount.

How do they handle those rapid cold fronts we sometimes experience. Temps dropping into the teens.  Just curious.

Bob,

Grass carp are just fine when we drop into the teens for a few days. Grass Carp are very cold tolerant. I'm unaware of grass carp ever dying in Texas or even Oklahoma from a cold front or cold water.