Yellowing and/or mushy leaves are the most common symptoms of overwatering.
Overwatered plants wilt like dry ones. The whole plant or branch tips may wilt.
When roots are constantly wet, they become stressed and are more susceptible to a variety of disease pathogens that cause the roots to rot.
Steinkopf says indoor plants, "Fungus gnats may occur before or after yellow leaves. They indicate too-moist potting medium."
Overwatering outdoor plants takes a lot of water, but it happens. Deep watering less often is preferable than light watering often.
If the plant's soil is saturated but it still has wilted or yellowing leaves, it may be overwatered.
Sometimes when a plant is getting too much water, its leaves may start to turn brown and drop off.