The Charles River, which never smells very well anyway, has a particularly bad odor this fall because of the drought, and will probably stay that way until the next big rain, according to Adam E. Sulesky, Director of the Sewerage Division of the Metropolitan District Commission.

It seems that the long dry spell in the Boston area has left the Charles low and relatively stagnant. At the same time, salt water has been coming in through the dam at the mouth of the river. Since the salt water is heavier, it sinks to the bottom, preventing the normal turnover of the river.

As a result, the river has divided into a stagnant upper layer of fresh water and a deoxygenated lower layer of salt water. The sewage which is drained into the Charles falls to the bottom, where it decomposes. Since there is not enough oxygen, this decomposition produces hydrogen sulfide, which gives off the now-familiar smell or rotten eggs.

MDC Can't Do Much

Despite a long-range improvement program that has been under development for 14 years, the MDC is only partially able to improve the situation. It is presently trying to limit the flow of salt water and sewage into the river, and is pumping fresh water in from Lake Cochituate.

The odor, which is noticeable as far inland as Mass. Ave., is particularly bad in the Harvard area because the Charles is shallower there.