We asked water imagery of Lake Union by a questionnaire to 64 houseboaters and 37 uplanders. The result showed that houseboaters recognized more clearly various water characteristics and feelings about Lake Union than uplanders. Houseboaters gave higher evaluation to attractiveness and value of the lake. Comparing imageries obtained by the questionnaire, results of interview, and observation of the environment, we obtained physical characteristics of the environment which explained the causes of houseboaters' water imageries. They were 1) a lake and houseboats, 2) nature adjacent to a houseboat--visiting wild animals and four seasons, 3) a floating deck close to the water, and 4) a small lake. Majority of uplanders who could see a part or all of the lake rated it very attractive, whereas less than half of those who could not do likewise.