A lake in a dream usually reflects a calmer, more contained emotional state than an ocean or river -- feelings you've found some stillness with, at least for now. A clear, quiet lake can point to unhurried reflection and inner peace, while murky or disturbed water may suggest that stillness is more fragile than it looks.
Give not judgment before thou knowest the intention of the querent; for many ask they know not what, nor can they express what they intend. - William Lilly (1602.-1681.)