The aquatic and semi-aquatic plant communities of Utah Lake, Utah County, Utah are discussed. This discussion includes the methods of describing and delimiting the major vascular plant communities, the descriptions of the present existent communities, and the determination of the vegetational changes, particularly since 1925. The vegetation around Utah Lake is divided into plant communities. Each community is discussed using: (a) quantitative data, (b) field observations, (c) general and specific locations of the community, and (d) interrelationships and trends of the community. Historical vegetational changes of Utah Lake plant communities are discussed. In this discussion, the plant communities described by Cottam in 1925 are examined in broad outline and then in detail. In 1968, twenty-nine plant communities had developed from fifty-six per cent of the associations and twenty-nine per cent of the societies that were described by Cottam in 1925.

Provo Bay of Utah Lake, Utah, receives the effluents from farms, industry, and three cities. In order to determine the effects of these effluents, eleven stations were established throughout the Bay. At weekly intervals from June 19 to October 26, 1970, and monthly thereafter until March, 1971, the water at these stations was sampled for dissolved oxygen (DO}, carbon dioxide (CO2), turbidity, pH, phosphates, nitrates, biochemical oxygen demand (BOD) and coliform bacteria. Due to intense algal blooms, the quality of the water changes as it passes through Provo Bay. Average values for the inflow, mid-Bay, and point of discharge respectively during the summer are as follows: DO, 5.4--10.2--6.9 mg/l; CO2, 38--0--6 mg/l; turbidity, 19--80--57 Jackson Turbidity Units; pH, 7. 5--9. 0--7. 2; phosphates, 3. 62--0. 94--0.15 mg/l; nitrates, 0.71--0.08--0.00 mg/l; BOD, 17--27--9 mg/l; and coliforms, 31,000--31--0/100 ml. These results indicate that during the summer Provo Bay is acting as a tertiary treatment pond for the effluents which it receives.