The pair had spent Sunday near the Ackers centre in Small Heath when they were approached by three youths.
One pulled out a gun and grabbed the dad's silver mountain bike. As the thugs rode away they said they would 'shoot' the victim if he tried to follow them or call the police.
The dad-of-two, who does not wish to be named, had been fishing on the spot, near Golden Hillock Road, with his daughter since 10am, when the incident happened around 3.34pm.
He said: "We were approached by three lads and one of them managed to block me.
"I told my daughter to run and they pulled out a gun.
"I tried to attack them with my fishing rod but they ran off with my bike.
"Of them said to me, 'If you follow us, we will shoot you.'"
The 38-year-old said : "It was over in a minute. They ran off with my bike towards the Ackers Centre.
"I was frightened for my daughter's safety. Police sent armed police to the park and they took us home.
"It was serious, one of us could've been shot. It's had a very devastating impact."
The victim said the gun was 'distinctive' and jet black' like a P40.
"I'm never going back there again." he added.
"I've been told that it's happened a few times along that stretch of canal."
A West Midlands Police spokesman said: "We received a call yesterday (19 Sept) at 3.45pm from a man reporting he'd been robbed of his bike and fishing tackle while on Tyseley Canal.
"The man, who was with his daughter, said he was threatened with a pistol before the offenders made off towards Ackers Centre.