Site locations for the TIME and LTM programs where there is monitoring data. The TIME network design is based on the random, probabilistic methods developed for the Environmental Monitoring and Assessment Program (EMAP) in which sites are statistically based, thereby allowing population estimates to be developed from a random design of selected lakes and streams. The sampling schedule for TIME is once per year (July-early September) and results are used to estimate trends in chronic acidification and answer questions like: "How many acidic lakes are there? What is the trend in the number or proportion of lakes which are acidic?" The LTM network consists of hand-picked sites lakes and streams from various acid sensitive classes. They are sampled 3 to 15 times per year with a higher proportion of sampling conducted in the spring which coincides with higher rates of runoff (e.g., snow melt) and higher stream flows. This information is used to characterize how the most sensitive of aquatic systems in each region are responding to changing deposition, as well as giving information on seasonal chemistry and episodic acidification. TIME and LTM sample the same list of chemical variables and are designed to be mutually beneficial.