What type of plants live in lakes? and what type of animals?

Question

How biologically diverse is a lake?

Answer 1

A nice book could be written answering your questions!  To answer your first question, plants found in lakes will be modified to survive in a low oxygen content (floating leaves, highly dissected underwater leaves). Water lilies, lotus, cattails, various rushes, and duck weed are common water loving plants.  

Animals will vary with the climate.  There will be differnet animals in the south than in the north especially types of fish.  

There are lakes with varying amounts of nutrients available.  A high mountain lake will have very little growth in it due to the lack of nutrients.  Fish in those lakes are often stunted in size due to the lack of food.  The water will be crystal clear due to the lack of phytoplankton and zooplankton.  Lakes in warmer climates and  with more nutrients will support much more life.  One of my favorite activities as a biologist is exploring the life in various bodies of water.  An alkaline lake will have much different creatures in it than a swamp in Georgia!

Hope this helps.  To get more specific requires much more space and time than what I have!