My tree stood in water after the yard flooded and now it looks sick — what should I do?

Standing water or spongy, saturated soil over the root area for days at a stretch. Leaves yellowing between the veins, and wilting while the ground is still wet — wilting in wet soil is the tell — plus curling, drooping, and early drop. New shoots come in short, and some species redden early. Later: dieback at the top, water sprouts on the trunk, a sour smell from the soil, and mushrooms at the base. In severe cases soil cracks in an arc on one side of the trunk or the root plate lifts, which is a different and far more urgent sign. Roots need oxygen, and water fills the pore space that delivered it. The tree is suffocating rather than drowning, and fine absorbing roots die within days in oxygen-free soil, so the tree shows drought symptoms while standing in water. Past the root loss, saturated soil shifts chemically and favors water-mold pathogens like Phytophthora that attack the root collar. Saturated soil also grips a root plate far more weakly than dry soil does, so a tree that was stable last week may not be this week.