Valuing the improvement of water quality in Iowa lakes is the objective of this dissertation. In the first two essays, the focus is combining revealed preference and stated preference data from an intercept survey at a northcentral Iowa lake. In the first essay, the contingent behavior trips which are contingent on the price (i.e. travel cost) of the recreation trip are combined with observed trips. However, since this data set was collected on-site, the primary purpose of the first essay is to consider controlling for on-site sampling with a panel data set. A count data model is employed, specifically a mixed Poisson regression model, with a more flexible log-normal mixing distribution rather than the standard gamma distribution. This essay shows the importance of correcting for on-site sampling, as the adjusted average fitted observed trips and contingent trips decrease significantly, resulting in lower annual consumer surplus estimates.;The second essay uses a continuous model jointly estimating three data sources, observed behavior and contingent behavior trips, and contingent valuation data, following Huang, Haab, and Whitehead's 1997 article in the Journal of Environmental Economics and Management. This essay extends Huang, Haab, and Whitehead's analysis by correcting their joint model for on-site sampling.;The final essay uses two extensive data sets, one economic (a random sample of 4,500 Iowan's trip behavior to 129 of Iowa's principal lakes in 2002), and one ecological (14 physical water quality measures for the 129 Iowa lakes for 2002). This essay analyzes Iowan's responsiveness to variation in physical water quality measures. A repeated mixed logit model is employed and the results show that Iowan's do consider the physical condition of the lake water when choosing which lakes to visit. In particular, decreased water clarity and increased nutrient concentrations leads to fewer trips. Lastly, welfare scenarios were calculated indicating Iowan's highly value water quality improvement, but with limited resources, they would prefer a few more lakes with superior water quality over all of the impaired lakes being adequately improved.