Gyro-copter pilot reported a flight control problem during initial climb requiring an off-airport landing.

Narrative

Take off was uneventful as was initial climb to 50 feet. I quickly noticed we slowed to 50 knots and our rate of climb stopped; I ensured I had full power applied and tried to physically push the stick forward and the stick did not seem to want to move forward. I tried to push the controls forward hard but was unable. Airspeed dropped to 45 knots and the gyro-copter started to descend. I shook the stick; loudly exclaimed to the PAX (passengers) to make sure they were clear of all controls and pushed hard forward and normal stick feel was returned. At this point the airspeed had dropped to 40 knots and my efforts with full power and stick forward were slowly building airspeed but not fast enough to climb and avoid hitting trees on the departure end with not enough distance to land before a fence. I made the choice to turn towards a clearing to my left in the hope that the extra space would allow me to regain some lift and facilitate either a climb to clear any obstacles or a clear area to land. When it became obvious that a landing was unavoidable; I leveled the roll; maintained full power; and maintained a nose down attitude to try and gain as much speed for the round out and flare. I landed in a grass area between two ponds but was unable to stop before the second pond when the gyro-copter rolled over and came to rest in about 2-3 feet of water.