mo ▁River ▁is ▁usually ▁fro zen ▁from ▁early ▁November ▁to ▁mid - May , ▁however ▁safe ▁ice ▁movement ▁is ▁generally ▁from ▁mid - Nov ember ▁to ▁mid - A pril . ▁ ▁Geography ▁ ▁The ▁main ▁hydro graph ic ▁s lop es ▁near ▁the ▁O mo ▁River ▁are : ▁North ▁side : ▁Ass in ica ▁Lake , ▁Ass in ica ▁River , ▁Bro ck ▁River ; ▁East ▁side : ▁Com en cho ▁Lake , ▁Op ata ca ▁Lake ; ▁South ▁side : ▁M ild red ▁River , ▁C au p ich ig au ▁River , ▁Ch ib oug am au ▁River ; ▁West ▁side : ▁Ma icas agi ▁River , ▁M ons an ▁River . ▁ ▁The ▁O mo ▁River ▁origin ates ▁at ▁the ▁mouth ▁of ▁an ▁un ident ified ▁lake ▁( length : ▁ ▁alt itude : ▁) ▁in ▁the ▁Ass in ica ▁Wild life ▁San ctu ary . ▁This ▁source ▁of ▁the ▁river ▁is ▁located ▁at : ▁ ▁North ▁of ▁the ▁mouth ▁of ▁the ▁O mo ▁River ▁( con flu ence ▁with ▁the ▁Ma icas agi ▁River ); ▁ ▁N ortheast ▁of ▁the ▁mouth ▁of ▁the ▁Ma icas agi ▁River ▁( con flu ence ▁with ▁Ma icas agi ▁Lake ); ▁ ▁N ortheast ▁of ▁the ▁mouth ▁of ▁Go é land ▁Lake ▁( W as wan ip i ▁River ); ▁ ▁N ortheast ▁of ▁the ▁mouth ▁of ▁Mat ag ami ▁Lake ; ▁ ▁South ▁of ▁the ▁mouth ▁of ▁the ▁Not ta way ▁River ; ▁ ▁N ortheast ▁of ▁dow nt own ▁Mat