How do folks approach lakes they know little to nothing about?

I am hoping someone has some suggestions for how to fish a lake near a country place we have in Colombia. There is very little recreational fishing in the lake, but it was stocked with rainbow trout about a hundred years ago and has some pen based trout raising for local restaurants. I don’t know anything about the native fish population or the forage base. The lake is called La Cocha and is about 100,000 acres, ten miles long and three miles at its widest point. The average depth is about 250 feet and the surface water temperature is approximately 50 degrees year round. It is 1 degree North of the Equator at about 10,000 feet elevation.

I have a canoe down there and some light spinning tackle. We are planning to canoe the outlet river, a tributary of the Amazon called the Guamues for a couple of miles, until it gets too steep for an open canoe. We will have to paddle a few miles to the outlet and I want to troll a bit and see if we can catch anything. I am thinking about taking a portable Garmin Striker down and seeing if we can find some structure. What lures should we try? Deep diving plugs come to mind. I don’t know if there is a thermocline or if deep tropical lakes turn over, and I really have no idea where fish would hang out in a lake like this.

The shallows are quite reedy and we will have to give them a try too. Any suggestions on ways to approach a lake like this? Thanks. I will report back after our trip.

Whenever I approach a big alpine lake at altitude near the equator, ..oh wait... never mind. I never do that.
Start shallow, as active fish are shallow. Try to find local info. Ask a kid on a bike with a fishing rod. Otherwise, dang, that sounds great. Let us know what happens.

Thanks! I will report back. I think taking down a sonar will help. I am also trying to learn about evaluating rivers from topos and recognizing areas that are mainly class 1 and 2 rapids, but it is challenging. I have never seen a canoe or kayak in this part of Colombia, but there are a couple of rafting outfitters on the river Juanambu.