Kenya supplies more than 35 percent of the fresh-cut roses and other flowers sold annually in the European Union. This industry—which employs at least 90,000 workers, most of whom are women—is lucrative but enduringly controversial. More than half the flowers are grown near the shores of Lake Naivasha, a freshwater lake northwest of Nairobi recognized as a Ramsar site, a wetland of international importance. Critics decry the environmental side effects of floriculture, and...