Overwatering tomato plants can be identified by a few signs. Wilting and yellowing of the leaves is one indication that too much water has been given to the plant. The soil may also become soggy or muddy, which is another sign of overwatering. Additionally, if you notice any fungal growth on the leaves or stem it could be an indicator that your tomato plant has been overwatered. Lastly, root rot caused by too much moisture in the soil can cause stunted growth and eventual death of the plant.