SMA PLT ON DEP AT SEAPLANE FACILITY HAS ACTUAL MIDAIR COLLISION WITH ACFT DEPARTING OPPOSITE DIRECTION.

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I CONTACTED THE TWR AND REQUESTED A W TKOF. ANOTHER ACFT CONTACTED THE TWR AND REQUESTED A SE TKOF WITH AN E OPTION. TWR ADVISED ME OF THE WIND FROM THE SE AND ASKED IF I STILL WANTED A W. I ADVISED THE TWR I STILL WANTED A W. TWR ADVISED ME TO HOLD AND ADVISE WHEN READY. THE TWR CLRED THE OTHER ACFT FOR TKOF SE. I MUST HAVE RECEIVED THE LAST PART OF THAT XMISSION AND THOUGHT IT WAS FOR MY ACFT. BOTH ACFT ARRIVED OVER MID-FIELD ON A COLLISION COURSE. I SAW THE OTHER ACFT ABOUT 2 SECONDS BEFORE CONTACT AND IMMEDIATELY MADE A 90 DEG BANK TO THE L AND DOVE THE ACFT. I DID NOT THINK I HIT THE OTHER ACFT; BUT UPON LNDG I OBSERVED DAMAGE TO MY AILERON AND TRAILING EDGE OF THE WING. THE OTHER ACFT DID NOT SEE MY ACFT AND HE THOUGHT HE HIT A BIRD. THE TWR DID NOT ADVISE EITHER ACFT OF THE INCIDENT OR DID NOT ADVISE EITHER ACFT TO ABORT BECAUSE OF CONFLICTING TFC. AFTER LISTENING TO THE TAPE RECORDING I FEEL THE CTLR WAS VERY BUSY BECAUSE SHE WAS CTLING HVY JETS AT INTL AS WELL AS LAKE HOOD SEAPLANE BASE AND LAKE HOOD STRIP. ALSO THERE WERE MISSING CALLS I MADE THAT DID NOT APPEAR ON THE TAPE. I FEEL SOME XMISSIONS WERE BLOCKED AND A MISUNDERSTOOD CLRNC WAS RECEIVED.