sql query on multiple contains

Greetings.
I am trying to make a query which builds a table that has a 'present' or a NULL in each column of whether or not a point is within that polygon. I have a polygon file of waterbodies and a point file of invasive species data. I want to make a table that shows which invasive species are known to be present in the waterbody. So far I have come up with the following:

SELECT DISTINCT
wi_ogaa_harvest_waterbodies.mwbc,
wi_ogaa_harvest_waterbodies.county,
wi_ogaa_harvest_waterbodies.lake,
(CASE WHEN invspp_occurrence_data.tsn_char = '81339' then 'present' else NULL end) AS "Zebra_Mussel",
(CASE WHEN invspp_occurrence_data.tsn_char = '684624' then 'present' else NULL end) AS "Spiny_Waterflea",
(CASE WHEN invspp_occurrence_data.genus = 'Myriophyllum' then 'present' else NULL end) AS "Eurasian_Water_Milfoil",
(CASE WHEN invspp_occurrence_data.tsn_char = '39007' then 'present' else NULL end) AS "Curly_Leaf_Pondweed",
(CASE WHEN invspp_occurrence_data.genus = 'Heterosporis' then 'present' else NULL end) AS "Heterosporis"
FROM inland.wi_ogaa_harvest_waterbodies
JOIN invasive_species.invspp_occurrence_data ON ST_Contains (wi_ogaa_harvest_waterbodies.the_geom, invspp_occurrence_data.the_geom)
ORDER BY county, lake

This seems to work correctly, but for each record (lake) that has a species present a new line is formed. For example, if a lake had all five species listed, the lake would be listed 6 times in the table (one line for each species present and one line for all NULLs). If I use GROUP BY, it returns errors unless I include all columns including "invspp_occurrence_data.tsn_char" and "invspp_occurrence_data.genus" which puts me in the same spot I was without using GROUP BY.

Does anyone know what I am doing wrong or how to fix? Any help would be greatly appreciated.
Miigwech!
Dara