It's clearly a Hedychium/butterfly ginger. I don't think it would kill you, but this is not one of the gingers used in cooking. Since it is growing wild, I would think it is a species ginger rather than a hybrid. Because the flower is yellow, my first guesses would be Hedychium flavum (http://www.gingersrus.com/DataSheet.php?PID=3209) or Hedychium flavescens (http://www.gingersrus.com/DataSheet.php?PID=3208). I don't know if either of them is established in the wild in Hawaii. If not, it could be anything, including a seed from a hybrid scattered by wildlife. The seeds of many riverbank plants float and use the waterway to disperse the plant. You might consider what is on upstream from the plant you found.

Here is a link to the Gingers-R-Us Hedychiums chart with many links to species and hybrids: (http://www.gingersrus.com/hedychium.php) Click on the red number in the first column. I think it is the best centralized resouce on butterfly gingers.

Hi bornplaydie, I just got back today from Kauai - what a wonderful place. You sure are lucky living there. We hiked the trails in Waimea Canyon and saw lots of Hedychium flavescens (possibly H. flavum) growing everywhere along the streams. There is much confusion between that species and H. flavum, but the one I saw there had the wider bracts that I have always understood to be H. flavescens. That one, and also H. gardnerianum (another yellow) and H. coronarium (white) are among the worst of the invasive exotic plants in Hawaii. They have spread all through wild areas displacing native Hawaian plants.

As Planterric said, it is not used for cooking and does not have the same flavor as the common cooking ginger, although none of the Zingiberaceae are known to be poisonous.