Narrative:

Climb out of ZZZ; passing 2000 MSL for 4500 MSL VFR contacted approach (for class C passage. Heading out ZZZ was a heading of 187 for 10-15 miles; then a planned crossing [a large body of water] after gaining at least 3500 MSL for safe crossing (needed glide distance w/o floatation).at 2100 MSL climbing ATC directed an 'at/below 2500 MSL'. Student pilot replied 'unable 2500 after 60 seconds'. ATC did not acknowledge; but then gave two vectors to what I (the CFI) believed to be the other conflicting aircraft). 2 minutes later (approaching 3000 MSL) ATC queried our altitude and repeated the 2500 MSL restriction. I replied (as CFI) to ATC that we were unable to maintain that altitude because we needed to cross the water at a higher altitude. I heard in background a 'traffic alert' and the controller then called traffic '1-2 o'clock'. I sighted the traffic which was slightly moving in the windscreen; but not much. Possibly on collision course. I took the aircraft from the student and rolled a 45 degree right bank turn in VMC; reduced power and descended about 200 feet. I then called to ATC that traffic was in sight; no longer a factor; and I would keep in sight.I resumed the climb toward 4500 and crossed the water climbing through about 3300 MSL. After the crossing; ATC directed a call for debrief and I pledged to call after mission complete. Mission completed and I called ATC. Controller had gone home; so I followed the call in the morning as directed and debriefed ATC supervisor.

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Original NASA ASRS Text

Title: Cessna 150 Flight Instructor report being unable to comply with ATC altitude direction followed by an evasive maneuver for traffic.

Narrative: Climb out of ZZZ; passing 2000 MSL for 4500 MSL VFR contacted Approach (for Class C passage. Heading out ZZZ was a heading of 187 for 10-15 miles; then a planned crossing [a large body of water] after gaining at least 3500 MSL for safe crossing (needed glide distance w/o floatation).At 2100 MSL climbing ATC directed an 'at/below 2500 MSL'. Student pilot replied 'unable 2500 after 60 seconds'. ATC did not acknowledge; but then gave two vectors to what I (the CFI) believed to be the other conflicting aircraft). 2 minutes later (approaching 3000 MSL) ATC queried our altitude and repeated the 2500 MSL restriction. I replied (as CFI) to ATC that we were unable to maintain that altitude because we needed to cross the water at a higher altitude. I heard in background a 'traffic alert' and the controller then called traffic '1-2 o'clock'. I sighted the traffic which was slightly moving in the windscreen; but not much. Possibly on collision course. I took the aircraft from the student and rolled a 45 degree right bank turn in VMC; reduced power and descended about 200 feet. I then called to ATC that traffic was in sight; no longer a factor; and I would keep in sight.I resumed the climb toward 4500 and crossed the water climbing through about 3300 MSL. After the crossing; ATC directed a call for debrief and I pledged to call after mission complete. Mission completed and I called ATC. Controller had gone home; so I followed the call in the morning as directed and debriefed ATC supervisor.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.