Signs of dehydration to watch for during exercise include feelings of increased thirst, dry mouth, and reduced urination frequency. Additionally, an unusual darkening of urine indicates a need for fluid intake. More severe symptoms can manifest as dizziness, fatigue, or headaches, all suggesting that hydration levels are low. Monitoring body temperature can also provide insight; overheating while not properly hydrated can lead to heat-related illnesses. It's crucial to prioritize hydration strategies like drinking before, during, and after exercise to maintain peak performance and avoid negative health effects.