No issues have ever been found, and it's unlikely they ever will be.
In the case of Roundup Ready, and similar herbicide resistant varieties, they are simply resistant to the chemical and it is not in the plant itself. This allows the use of a broad spectrum herbicide that's often less toxic to people and animals to be used. For example the lab rat tests have shown that glyphosate (Roundup) is less toxic than items such as table salt or aspirin.
The the other big GM trait is BT, which simply produces a bacteria with those initials. This bacteria damages the digestive systems to insects who eat it, and has never been found damaging to humans or other animals. If I'm not mistaken it is legal to spray the bacteria onto organic crops, as it's natural (they can not plant the GM varieties obviously). This is also much safer as most insecticides go after the nervous system, which works the same way as our nervous system does and can lead to exposure problems. I have also heard stories about how when Roundup first came out there were actually people who would throw a shot into a glass of orange juice and drink it just to show it's safety to people, as far as I know none ever served any ill effects, except for maybe a sour stomach right after. I wouldn't worry about any health effects if there was runoff after spraying into your pond, as it's likely less damaging than any other herbicides. It may hurt some seaweed, however with as quickly as it breaks down chances are it's close to gone by the time it's gotten there. Once again Roundup breaks down into inert molecules in the environment a lot faster than most others.
In short simply living near GM crops will not harm your health. Often GM traits are there in order to use fewer and often safer pesticides than would otherwise be used. Also remember any food-related technology undergoes extensive testing to make sure there are no direct links to human illnesses or anything of the sort due to the massive impact it could have. In fact it is harder to get a new pesticide approved for use than it is to get a new medicine approved due to the much larger scale of impact that it may have.