Improved soil conservation techniques and reduced erosion mean cleaner water and more trout with less stocking. It also means that there are more trout available now than at any time in the past 30 years. According to more than 2,400 DNR fish population surveys, the trout population in southeastern Minnesota has tripled since 1970 and the average number of browns more than 12 inches long increased from 26 per stream mile in the 1970s to 55 in the 1990s.
But a general population increase doesn't guarantee good fishing every time. Trout populations still tend to fluctuate from year to year as floods and other factors affect natural reproduction.
Three other factors: growth, fishing pressure, and habitat also affect trout populations, especially the number of large trout. Good growth and suitable habitat are needed for streams to support larger fish. Also, heavy fishing pressure and harvest can have a negative effect on trout size and numbers.