Tangled Mass on lake needing large equipment (8)
I believe the answer is:
materiel
'equipment' is the definition.
(I know that materiel is a type of equipment)
'tangled mass on lake needing large' is the wordplay.
'tangled mass' becomes 'mat' (I've seen this in another clue).
'on' is a charade indicator (letters next to each other) (in a down clue, letters appear on others).
'lake' becomes 'erie' (Lake Erie is one of the Canadian/US 'Great Lakes').
'needing' says to put letters next to each other.
'large' becomes 'L' (eg in clothes sizes).
'mat'+'erie'+'l'='MATERIEL'
(Other definitions for materiel that I've seen before include "Military equipment and supplies" , "Military baggage" .)