blue green algae

blue green algae

Improving water quality

Verspreiden Phoslock

Drijflaag blauwalgen

Bouwen zanddam

Zwanen in recreatieplas

Conclusions and follow-up actions

The research has brought us to the following conclusions:

  • Short term

Certain measures, like the sealing of certain areas of the water by oil screens or aerating the water generally give limited results. If circumstances are positive for algal growth over a longer period, algae levels are often undesirable for an intensive water exposure for humans and animals.

The integral approach, as was used for within the swimming area of the Groene Eiland appears effective. Measures are mainly source oriented.

This package has the following elements:

  • Keeping a high level of oxygen in the water in the swimming area

  • Aerating the water through the use of a pump

  • Increasing light permeation, by removing high plants at the south of the swimming area

  • Agreements with sport fishermen not to spread bait into the swimming area. (Fish bait contains a lot of phosphorus.)

  • Limiting the population of waterfowl (excrements contain a lot of phosphorus) 

  • Reducing the phosphorus content of the lake by spreading the phosphate binding product Phoslock

The mutual relationship between these measures is not as yet sufficiently researched. In other words: at this stage we don't know what the most effective combination of the mentioned measures would be.

 Also we don't know yet how large the safety margin is. In other words: how far should we go not to reach the undesirable levels for humans and animals in seasons with particularly favourable conditions for algae growth. 

  • Long term

It is known that blue green algae in general don't proliferate in undesirable quantities in water with sufficient current. The recreational area the Gouden Ham is now a dead branch of the Maas river, but with relative simplicity the area can again become a concurrent fairway of the river.

In consultation with the province Gelderland, Rijkswaterstaat Limburg, Management Association Gouden Ham, the Recreation Corporation Uiterwaarde, Civic Councel West Maas en Waal,  Radboud Universiteit Nijmegen, and DHV, this option is under investigation

On assignment of Rijkswaterstaat the engineering consultancy DHV has reviewed a number of scenarios in which residence time may have a major influence on blue green algae.

The two most promising scenarios will be worked out further. Due to financial and permit requirements, these measures aren't feasible in the short term. This spring a year round monitoring campaign has started to get a better insight in the developments of blue green algae. The results of this study are to be expected in 2009.

Tabel met analyse van fosfor in sediment zwembaai

Table summarising analysis of the sediment in the swimming area. (Click on the picture for an enlarged copy of this picture.)





Luchtfoto recreatiegebied De Gouden Ham

Birds view of recreational area 'Gouden Ham'




Kaart met locatie doorsteek voor doorstroming

By making a cut-through between recreational area Gouden Ham and river Maas somewhere in the red-circled area 
the Gouden Ham will become flowing water again.
Currently the best implementation of this option is researched.