Seasonal Turnover Leads to Brown Water

You may have noticed recently that parts of Smith Mountain Lake have turned a strange shade of brown, reminiscent of a cup of coffee and cream. If so, you have witnessed a seasonal process known as “turnover”.

This is a common phenomenon that takes place on many lakes, typically occurring any time from late fall to early spring. Despite how unappealing it looks, the process of turnover is actually beneficial to the ecosystem of the lake.

Simply put, turnover occurs when cold air temperatures cause the water near the surface of the lake to become cooler and denser than the water below it. The dense surface water sinks to the bottom, causing less dense water from the bottom to rise to the surface. This mixing process provides oxygen to aquatic life near the bottom of the lake while redistributing nutrients that have settled to the bottom during the year. The light brown color comes from the sediment that gets carried to the surface during this process.

When warmer weather arrives, the surface of the lake becomes warmer and less dense, and the mixing process ceases. This leads to a gradual depletion of oxygen near the bottom of the lake during the summer until the process repeats itself when the next cycle of turnover returns in the fall.