Answers are rivers, lochs, broads, lakes, meres, fens.
27. One of 3 in a board game (4)
34. Sometimes a silly idiot (4)
51. A feline space (8,5)
57. A girl from Hertfordshire (5)
61. Partly a herb with cold meat (6,5)
66. You will need a rigid opener for this lock (8)