Gergely, I am not in the least experienced, and I know nothing about Ohio,
but let me throw in my two cents worth of questions:
Is your water table high there? If not, it seems that your pond will drain
without a liner. If your yard is mucky, is it because of a concave surface?
Do you need to bring in a few yards of dirt to level it out first? Where is
your trench taking the water? Will it end up seeping back into the yard and
It seems to me that having a liner or not having one should not affect the
growth of algea too much. Algea grows in the sun. Water lilies or other
shade for the water, except for trees, whose leaves, I'm told are toxic
when they decay, should reduce the growth in your climate.
(Here in Texas algea grows by the time you can take a glass of ice water
across the porch!)
Are you planning on stocking fish or plants? How big will your pond be?