public Integer[] getParticipantsCount (Date d) {

		Integer pc[] = {0, 0, 0, 0, 0, 0};
		for (Trip t: getAllTrips(d)) {
			River r = t.getRiver();
			if (r != null) {
				int ww = t.getRiver().getWwTopLevel()-1;
				pc[ww] = pc[ww]+t.getGroupSize();
			}
		}
		
		return pc;
	}