(FORTUNE Magazine) – Willard Kaser presumably was just following company policy in managing Nabisco's Fleischmann yeast plant in Sumner, Washington. But in September a federal judge slapped him with a prison sentence -- a year and a day -- for violating the Clean Water Act. Kaser's conviction is an example of a legal phenomenon that is adding criminal charges to environmental civil ones. Felony provisions first appeared in federal environmental laws in 1976, but the Environmental Protection Agency did not add full-fledged criminal enforcement until 1982. Investigators began toting guns in 1984. Government prosecutors have since become more likely to insist that pollution is a violent crime because it shortens victims' lives; judges and juries are more inclined to go along. Several states have inserted criminal penalties into environmental laws. Criminal provisions in toxic waste laws are a lot more effective than fines imposed under civil statutes, according to officials. Says Richard Emory, criminal enforcement counsel at the Environmental Protection Agency: ''Administrative fines are seen by some people as part of the cost of doing business, but going to jail and being a felon is not.'' The threat of the slammer also squelches companies' objections to paying fines. Ohio assistant attorney general E. Dennis Muchnicki says companies ''are offering to pay any civil penalty if they can avoid criminal prosecution.'' Most corporate felons go to minimum-security prisons, where they can play all the tennis or miniature golf they like as long as they do menial work and get to bed by 11. That is small consolation to managers like Kaser -- college educated, a churchgoer, and a food bank volunteer -- who probably thought they were only doing their job.