Honda 2001 Civic Owner's Manual page 217

Clutch System
MAX
M I N
The fluid should be between the
MIN and MAX marks on the side of
the reservoir. If it is not, add brake
fluid to bring it up to that level. Use
the same fluid specified for the
brake system.
Low fluid level can indicate a leak in
the clutch system. Have this system
inspected as soon as possible.
Brake and Clutch Fluid
Maintenance