SWIMMING & ROWING:

IDIOM: put one's oar in rowing

MEANING 1: to put the oar of a boat into the water to help move it
SENTENCE 1: Please put your oar in now that we are away from the dock.

MEANING 2: to help in a group decision
SENTENCE 2: The boss said, " I want all of you to put put your oar in and think carefully about these business projections for next year."

IDIOM: rowing upstream rowing

MEANING 1: to row against the current or up the stream
SENTENCE 1: You need to row upstream a bit in order to catch fish.

MEANING 2: to be difficult, to be in a difficult position
SENTENCE 2: For the past year or two my marriage has been like rowing upstream.

IDIOM: keep one's head above water swimming

MEANING 1: to keep one's head above water by swimming or treading water
SENTENCE 1: Keep your head above water if you fall out of the boat.

MEANING 2: to stay ahead in one's work
SENTENCE 2: I have to work ten hours a day to keep my head above water.

IDIOM: swim against the tide, go against the tide swimming

MEANING 1: to swim against the tide or pull of the ocean
SENTENCE 1: You can get very tired and drown if you swim against the tide.

MEANING 2: to do something difficult, to do the opposite of everyone else
SENTENCE 2: I'm having trouble keeping up with my schoolwork. I'm swimming against the tide.