A long-standing hunch among conservation biologists that managing a national park for ecological integrity as a biodiversity reservoir runs counter to managing it as a recreation facility was the subject of a two-part study in Lake Nakuru National Park in Kenya in August 2015 to identify the spectrum of visitor behaviors that cause problems to wildlife and to the wildlife habitat in the park, to determine drivers of problem behaviors among park visitors, and to determine effectiveness of on-site park messages in managing visitor conduct in the park. The study involved survey research with a descriptive design. Part one of the study involved use of a self-administered, closed-ended, drop-and-collect questionnaire administered to 100 randomly selected security officers to identify visitor problem behaviors to both wildlife and its habitat in Lake Nakuru National Park and drivers of the problem behaviors among park visitors. The questionnaire return rate was 100% (n = 100, 80 males: 20 females). Data obtained was cleaned, coded, appropriately analyzed using descriptive statistics and the Statistical Package for Social Sciences (SPSS), and presented in frequency tables. Differences between means were tested at the 95% confidence level. Internal consistency among responses to clustered questionnaire items was evaluated by Cronbach’s alpha values. Visitor failure to conform to the park’s code of conduct was found to be rife and wide spectra of problem behaviors to both wildlife and its habitat exist. Overall, problem visitor behaviors constitute a major problem to wildlife and a minor problem to the physical environment. Animal harassment and environmental degradation were resultant impacts of problem visitor behaviors in the park. Key drivers of problem visitor behaviors included ignorance of the visitor code of conduct; influence from fellow visitor behaviors; failure to interpret park regulations; a “don’t care” attitude among visitors; and, the desire among visitors to make the most of their park visit. Part two of the study was aimed at determining the effectiveness of on-site “plea” and “sanction” messages on visitor conduct and involved incognito observations on 100 individual visitors at each of the four separate observation sites, each with a specific on-site message. Whereas sanction messages were more effective than plea messages in managing visitor conduct, the effectiveness of both message types was enhanced by including an interpretive segment in the message. Youths and groups were more prone to disregarding the on-site messages than adults and single visitors. The study finds visitor conduct as the weak link in managing Lake Nakuru National Park for ecological integrity and as a recreational facility and presents a realistic need for park management strategies that promote responsible tourism through effective visitor education and information programs to protect wildlife and its habitat from recreationists. More recreation ecology research is recommended.