不諳水性

不谙水性
bùānshuǐxìng
to not know how to swim; to not be a strong swimmer

CEDICT

Entry Composition

1 不 bù
  1. no; not so
  2. (bound form) not; un-
2 諳 ān
  1. to be versed in
  2. to know well
3 水性 shuǐxìng
  1. swimming ability
  2. characteristics of a body of water (depth, currents etc)
  3. aqueous
  4. water-based (paint etc)