By Marin County
The Marin County Flood Control and Water Conservation District has opened tide gates at Novato Creek to help alleviate a rotten-egg smell at Pacheco Pond, a 120-acre pond just west of the entrance to the Bel Marin Keys neighborhood in unincorporated Novato.
The district has received numerous calls in recent days about the pungent odors at the pond, which is just east of the Bel Marin Keys commercial district and just north of the Hamilton neighborhood.
What creates the smell? At this time of year it is common for shallow ponds to stratify into distinct layers based on temperature differences, locking the bottom layer of water away for months. With no circulation, the oxygen is quickly used up, resulting in an anaerobic (functioning without oxygen) digestion process that is loosely equivalent to that of a cow’s stomach.
Slow-moving anaerobic bacteria on the bottom use enzymes to ferment and digest the muck on the bottom. These bacteria produce waste products including carbon dioxide and hydrogen sulfide (the source of rotten egg smell).
Most of the year, no smell is noticeable because the buildup of stinky gasses stays locked away on the bottom. It is typical for ponds to “turn over” in the late summer months, releasing foul-smelling gases. To assist the pond with its natural digestion process, the Flood Control District has opened the tide gates at Novato Creek to improve aeration and circulation within pond.