What is a species of algae that grows best at low water temperatures?

"Snow algae" (fresh water) cause coloration in high mountains, polar regions and melting snow. These include Chlamydomonas nivalis, Chloromonas nivalis, C. brevispina and less frequently the genera Koliella, Raphidonema, Ulothrix and others. These are unicellular organisms with complicated life cycles (link #1). There are also unicellular algae and diatom chains reported among the organisms that thrive in arctic sea ice. Melosira arctica is one of these. (link #2).

Cold loving organisms are called "psychrophiles". A psychrophile is a type of extremophilic organism which thrives at what is considered to be unusually cold temperatures. They can be contrasted with thermophiles, which thrive at unusually hot temperatures. There are generally considered to be two groups of psychrophiles: "classic" psychrophiles and a second group that are sometimes referred to as psychrotrophs by food microbiologists. Classic psychrophiles are those organisms having a growth temperature optimum of 15°C or lower - and do not grow in a climate beyond a maximum temperature of 20°C. They are largely found in icy places (such as in Antarctica) or at the freezing bottom of the ocean floor. Psychrotrophs can grow at 0°C up through approximately 40°C and exist in much larger numbers than classic psychrophiles. They are of particular significance to food microbiologists as they can grow in refrigerated environments and cause food spoilage.