Avian botulism, a lethal disease for birds, has been found spreading throughout Tulare Lake. The disease is caused by bacteria that thrive in shallow, warm waters with decaying organic matter.  The bacteria that causes the disease is found naturally in wetland soil. But it doesn’t produce the toxin that causes the disease unless environmental conditions are right. As temperatures soared in the San Joaquin Valley over the past few months, Tulare Lake warmed, causing perfect conditions for the disease to spread.  Neighboring wildlife areas, such as the Kern National Wildlife Refuge, often have standing, shallow water for bird habitat.