Some of the first eerie signs of a potential health catastrophe came as bizarre deformities in water animals, often in their sexual organs.

Frogs, salamanders and other amphibians began to sprout extra legs. In heavily polluted Lake Apopka, one of the largest lakes in Florida, male alligators developed stunted genitals.

In the Potomac watershed near Washington, male smallmouth bass have rapidly transformed into “intersex fish” that display female characteristics. This was discovered only in 2003, but the latest survey found that more than 80 percent of the male smallmouth bass in the Potomac are producing eggs.

Now scientists are connecting the dots with evidence of increasing abnormalities among humans, particularly large increases in numbers of genital deformities among newborn boys. For example, up to 7 percent of boys are now born with undescended testicles, although this often self-corrects over time. And up to 1 percent of boys in the United States are now born with hypospadias, in which the urethra exits the penis improperly, such as at the base rather than the tip.