For the best time to trek to Gosaikunda Lake, we should consider about the weather condition. Autumn (Sept-Nov) and spring (March-May) is the best season for trekking in Himalayas and same to Gosaikunda. Monsoon rain may affect the trek in summer (June-Aug). You can also trek in winter but temperature could be most harsh for most trekkers. Trekking in monsoon can be good for botanical keens as we can see the colorful flowers of alpine flower in higher places. And trekking in summer are quiet and there are less trekkers.