(i) This poem was actually written back in the 1980s, although it was not published until posted online in 2004. (Somewhere back in the 1980s I pretty much gave up trying to get my poetry published in order to focus on my novels.) These days, I tend to make an effort to use standard American spelling, but I've kept this poem in the New Zealand English in which it was originally written.
(ii) The setting of the poem is the North Island of New Zealand; I don't remember the exact location, but it's somewhere south of Auckland and to the east, quite a long way south of Auckland, heading (I think) in the direction of Rotorua.
(iii) The plastic of a tent fly is the "skin" which is keeping the dew just above my face. (A "tent fly" is basically just a rectangle of nylon equipped with eyelets and strings; it is designed to sit above a tent to keep off rain, but, at a pinch, if conditions are right it can be used as a substitute for a tent.)
(iv) The "frozen engines" are those of the cars which provided transport to the river.
(v) A "hydro-station" is a hydroelectric station, that is, a power station (a large electric generator, the kind you use to generate electricity to power cities) fed by water from a dam. The water is penned up behind the dam when demand for electric power is low (for example, at first light, when everyone in the big cities is still asleep) and then is released (to generate electricity) when demand is higher. Consequently, the level of water in the river rises and falls, and so the river is "tidal".
(vi) The river "steams" because there is geothermal water running into it from more than one geothermal source; it is this geothermal water which in places makes the river warm, and which releases a smell of "sulphur" - or, in American English, "sulfur". The "hot pool" which "bubbles" is being fed by some source of geothermal water - that is, water which has come from deep underground, and which has been heated by the inner heat of planet Earth itself.
(vii) The "sandfly" is a small black fly commonly found in New Zealand by rivers and lakes. It bites. There are not all that many sandflies in the North Island (the setting of this poem) but in the rain forests of the South Island they can, in places, be found in formidable numbers. (And here there is a tale I could unfold ... but, out of consideration for the tourist industry, I won't.)
(viii) The "canoes" in question are kayaks, the kind of canoe you sit in and paddle with a double-bladed paddle, not the kind of canoe you kneel in.
(ix) I "hope that no herbicide feeds me" because New Zelanders are great fans of spraying herbicide on any undesirable plant, and blackberry is (I think) considered a noxious weed, to be exterminated where possible. Consequently, eating wild blackberries was a bit of a gamble. The "timbers" of the "forest" were, if memory serves, the pine trees of some commercial forestry operation.
(x) One event not recorded in the poem makes this weekend trip to a river particularly memorable for me. When everyone was packing up to go home, I was standing with my back to a trash fire when there was a loud explosion. I felt a searing pain on the back of my legs. Looking at the backs of my legs, I saw they were inexplicably covered with orange. It took me a few seconds to figure out that some idiot had left a can of spaghetti in the fire, and the can had overheated and had exploded. Fortunately, no serious damage was done. If I'd been sitting facing the fire, though, it might have been another story.
(xi) This was my one and only experience of kayaking. Consequently, I can't precisely define a "spray-skirt." I think, from memory, that the kayak has an opening in which you sit, and that the "spray-skirt" is some kind of material (nylon, perhaps) which is used to cover the opening and prevent water from dripping in.
(xii) When I first wrote this poem, it would never have occurred to me to imagine that perhaps it might need notes. Everything in the poem was obvious. But that was then and this is now. As I write these notes, it's January 2004, and I'm sitting in Japan, in Yokohama, using a computer which is plugged into a national grid which relies very heavily on nuclear power plants rather than hydroelectric power (though Japan has its fair share of those.) The poem is being posted on the Internet, and the audience is (potentially) just about anyone anywhere on planet Earth. I don't now automatically assume (unthinkingly) that everyone knows what a "sandfly" is, for example, or why "Warm water" might be tainted with "sulphur."