The giant garter snake is found in California, from Butte and Glenn counties in the north, to Fresno County in the south. Giant garter snakes inhabit marshes, sloughs, ponds, small lakes, small streams and other waterways. They are also found in agricultural wetlands such as rice fields and irrigation and drainage canals. In order for the giant garter snake to be able to hunt and escape from predators, the wetlands should have tall vegetation growing in the water, at the water’s edge and on the banks. Even though the giant garter snake is thought of as an aquatic snake, the adjacent uplands are extremely important to them as they use these uplands to bask or find shelter for the winter. The giant garter snake overwinters in burrows made by small mammals, including ground squirrels and other rodents.

Giant garter snakes appear to be most numerous in rice growing regions. The rice fields provide a mix of habitat elements that the snake uses throughout the year. In the spring and summer, rice fields are flooded for rice production. The snake can be found in these flooded fields feeding on small aquatic species and using the vegetation for cover. The artificial levees create great upland habitat for the snake as parts of the levees are always dry. This is important during the winter months when rice fields are typically flooded again for waterfowl. Burrows found in these dry areas provide excellent shelter for the snake to use for overwintering. The giant garter snake is not found in or around larger rivers due to the presence of predators.

The giant garter snake is an opportunistic hunter, feeding primarily on aquatic prey like small fish, tadpoles and frogs. Giant garter snakes take advantage of small pools of water that trap prey like fish. The snake specializes in ambushing prey underwater and has been observed dragging its prey out of the water to be consumed.

The giant garter snake is active during daylight hours from early spring to late fall. They are dormant or in a state of low activity from November to mid-March. Giant garter snakes breed from March through April. The snake does not lay eggs; it gives birth to live young. Young snakes are born from mid-July to early September in litter sizes range from 10 to 46 individuals. At birth, the young immediately scatter into dense cover and absorb their yolk sacs. Then they begin foraging on their own.

The giant garter snake is one of the largest garter snakes that can grow at least 63.7 inches (162 centimeters) in length.

The giant garter snake is olive to brown with a cream, yellow or orange stripe running down their back, and two light colored stripes running along each side. They can also have a checkered pattern of black spots between the back and side stripes. Individuals in the northern Sacramento Valley tend to be darker with more pronounced stripes. The snake’s underside ranges in color from cream to orange to olive brown to pale blue, with or without markings. When giant garter snakes are about to shed their skin, their patterns and coloration may be obscured.

Giant garter snakes breed from March through April. The snake does not lay eggs; it gives birth to live young. Young snakes are born from mid-July to early September, and litter sizes range from 10 to 46 individuals. At birth, the young immediately scatter into dense cover and absorb their yolk sacs. Then they begin foraging on their own.