Hello, can I swimm in the lake? And is there any really good place to swimm?

We will be in Dali around 13th of June and our plan is to rent a bike and bike around the lake (which direction is the easier to choose, clockwise or?) and also have a little swimm in the see. I expect the water to be around 17C to it is quite good. Yeah and please, can you tell me where and for how much can we rent a proper bike wich derailleur? Thank you in advance for all the answers!! Cheers, Hana, Czech republic