Le acque del Lago di Costanza sono troppo pulite, manca plancton e i pesci non hanno di che nutrirsi. La loro quantità è di conseguenza in calo, in particolare quella dei coregoni e dei pesci persici. A denunciare nuovamente questa situazione, venerdì, sono i 134 pescatori professionisti svizzeri, tedeschi e austriaci, che l'anno scorso hanno visto le loro catture calare del 16% a 465 tonnellate. È stato l'anno peggiore dal 1954 a questa parte e la sopravvivenza della categoria è minacciata.
Il rimedio consisterebbe nell'immissione di fosfati, che favoriscono la crescita delle alghe. Tutti gli Stati e i cantoni che si affacciano sul lago hanno già respinto l'ipotesi di "concimarlo". L'Ufficio della protezione dell'ambiente turgoviese fa notare che più alghe richiedono più ossigeno, che già scarseggia, e anche questo non sarebbe un bene per la popolazione ittica.
pon/RG
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