Tides do not influence water levels as much in an estuary environment. The water is brackish and varies in salinity there.
Reading this will help you:
http://fds.oup.com/www.oup.com/pdf/13/9780198525080.pdf
what are contrasts between a marine and estuarine environment?
3 answers
Can I also mention in my answer that an estuarine environment is part of a marine environment?
I do not recommend doing that. One is not a subclass of the other.