Every answer is water related - some do not have any letter counts
Last 4 please can you help?
27. Hoar frost or frozen dew
65. A marking produced by water trickling down a beach (8)
68. Leptospirosis
77. A chalk stream which flows intermittently (6)
from google
Hoar frost might form as liquid dew that has subsequently frozen with a drop in temperature, which is then known as silver frost or white frost.
Granny, Leptospirosis is known by many other names including Weir's disease, Canicola fever, Hemorrhagic jaundice, Mud fever, and Swineherd disease.
So Weir's disease then since Weir relates to water. (or maybe Mud fever but Weir is better)