Videos uploaded to YouTube show large groups of people chanting slogans including, "Whoever stands aside and doesn't do anything is a coward."
The authenticity of the videos cannot be independently verified.
Eyewitnesses told the BBC that police arrested "dozens" of protesters and beat several others with batons.
In September, Iranians took to the streets of Orumieh to protest the dire condition of the lake.
Lake Orumieh, a salt lake located in Iran's East Azerbaijan and West Azerbaijan provinces, is drying up and turning into a salt marsh.
WATCH: User-generated YouTube video of protests in Orumieh
Late last year, RFE/RL photographer Abbas Atilay traveled to Orumieh to photograph the lake.
We will keep this post updated throughout the day. If any reader has more information -- photos, videos, eyewitness accounts -- please mention us on Twitter (@RFERL or @RadioFarda_) or send an e-mail to firstname.lastname@example.org (Azǝrbaycanca materiallar da qǝbul olunur; لطفا نظرات خود را هم به زبان فارسی).