May need some “fencing” to help guide them into that trap in open water that I am assuming your boat slip is in. I’m not talking about hardware cloth or dog fencing. I’m just talking about SOMETHING to make a wall that is big on one end and tapers into your trap. You have to MAKE them go in. Is your boat slip a floating dock? If so may try the trap tight against one of the floats and let that float guide the minnows to the mouth of your trap. Or you could try next to the bank and the the edge of your bank be your “guide or fencing”. I am saying this because I trap predators a lot and I have to fence them down into my sets. But I do notice minnows and almost every creature scales “walls” per say to get from point A to point B.

Like me a mouse trap for instance. U put them against walls. The mice travel along walls and will find your trap easily. Where as if u stuck it into the middle of an open room if u did catch one you would be lucky but chances of catching 2 are slim. I hope I helped.